Silicone Rubber Mechanical Properties: Tensile, Elongation, Tear Strength and Hardness Explained

For OEM design engineers and material specialists, selecting silicone rubber requires a clear understanding of its core mechanical properties. These parameters dictate how a seal, gasket, or molded component will perform under real-world loads, temperature excursions, and cyclic stresses. This article breaks down tensile strength, elongation at break, tear strength, hardness, compression set, and stress relaxation, providing typical ranges, test methods, and engineering examples to guide material selection for automotive, medical, electronics, food-contact, and industrial applications.

Why Mechanical Properties Define Silicone Rubber Performance

Silicone rubber’s versatility stems from its unique polymer backbone, but mechanical properties ultimately determine suitability for a given function. Tensile strength measures the maximum stress a material can withstand while being stretched before failure, directly impacting seal integrity in high-pressure hydraulic systems or pneumatic actuators. Elongation at break indicates how much the rubber can deform before rupturing, crucial for dynamic seals in reciprocating pumps or vibration isolators that experience large strains. Tear strength, measured in kN/m, quantifies resistance to crack propagation—a critical factor for gaskets subjected to flange misalignment or sharp-edge contact in electronics enclosures. Hardness, typically reported as Shore A, influences sealing force, installation ease, and resistance to extrusion; softer grades (20‑40 Shore A) conform well to irregular surfaces in medical device housings, while harder grades (60‑80 Shore A) resist extrusion in high-pressure oil seals. Compression set and stress relaxation, though not explicitly requested in the heading, are intrinsically linked to long‑term performance: a material that permanently deforms under constant load will lose sealing force, leading to leaks in fuel systems or coolant loops. Engineers must evaluate these properties together, as optimizing one (e.g., increasing tensile strength via fillers) can adversely affect elongation or compression set. Newsil supplies HTV, LSR, and custom‑compounded silicone rubbers with certified mechanical property data per ASTM and ISO standards, enabling data‑driven decisions for demanding applications.

Tensile Strength, Elongation at Break and Tear Strength

Tensile strength for silicone rubber varies significantly by formulation and processing method. High‑temperature vulcanized (HTV) grades typically range from 5 to 12 MPa, while liquid silicone rubber (LSR) grades fall between 5 and 10 MPa, reflecting differences in polymer chain length and crosslink density. For example, a platinum‑cured HTV compound reinforced with fumed silica might achieve 10.5 MPa tensile strength per ASTM D412, suitable for high‑pressure brake system diaphragms. Elongation at break complements tensile strength, showing how much the material can stretch; HTV silicones commonly exhibit 200‑800% elongation, whereas LSR grades often reach 300‑900% due to their lower viscosity and finer filler dispersion. A medical‑grade LSR with 650% elongation (ASTM D412) is ideal for peristaltic pump tubing that undergoes repeated flexing without cracking. Tear strength, measured using ASTM D624 (die C or B), typically spans 15‑50 kN/m for standard silicones. A tear‑resistant HTV compound containing specialized silica fillers can reach 45 kN/m, preventing crack growth in gasket corners exposed to thermal cycling in automotive exhaust manifolds. Conversely, a soft, low‑durometer LSR for keypads might exhibit 20 kN/m tear strength, adequate for low‑stress flexing but insufficient for high‑abrasion environments. Engineers should note that increasing tensile strength via higher filler loading often reduces elongation and can increase tear resistance up to a point, after which agglomeration may degrade performance. Balancing these properties is essential for components like dynamic O‑rings in aerospace actuators, where both high tensile strength (>8 MPa) and elongation (>500%) are required to survive pressure spikes and large deflections.

Hardness, Compression Set and Stress Relaxation Behavior

Hardness, measured per ASTM D2240 using a Shore A durometer, directly affects sealing force and installation characteristics. Silicone rubber hardness spans 20‑80 Shore A, with softer grades (20‑40 Shore A) used in medical device seals requiring low insertion force, and harder grades (60‑80 Shore A) selected for hydraulic piston rings resisting extrusion under 150 bar pressure. For instance, a 30 Shore A LSR provides gentle contact for a wearable sensor patch, while a 70 Shore A HTV compound maintains seal integrity in a turbocharger oil return line. Compression set, evaluated per ASTM D395 (Method B, 22 h at 175 °C), indicates the percentage of original thickness not recovered after prolonged compressive load; low compression set (<15 %) is vital for long‑term sealing in HVAC gaskets exposed to sustained clamp loads. A premium HTV silicone with post‑cure optimization can achieve 8 % compression set after 70 h at 200 °C, ensuring minimal leakage in industrial furnace door seals. Stress relaxation, often assessed via ASTM D573 (heat aging) combined with constant‑strain measurements, quantifies the decay of sealing force over time; silicones generally exhibit moderate relaxation, but formulations with optimized crosslink density can limit force loss to <10 % after 1 000 h at 150 °C, critical for electrical connector seals in under‑hood automotive applications. Hardness also influences tear resistance and elongation—softer silicones tear more easily but stretch further, while harder grades resist tearing but may crack under cyclic bending. Engineers must consider the interplay: selecting a 50 Shore A silicone for a food‑processing valve gasket balances adequate sealing force (≈0.8 MPa at 20 % strain) with acceptable compression set (<12 %) and tear strength (>30 kN/m) to withstand cleaning‑in‑place (CIP) cycles at 120 °C. Newsil’s technical data sheets provide certified values for these properties, allowing precise matching to application requirements across the automotive, medical, electronics, and industrial sectors.

Understanding the interplay of tensile strength, elongation, tear strength, hardness, compression set, and stress relaxation empowers engineers to specify silicone rubber that delivers reliable performance throughout a product’s lifecycle. By referencing standardized test methods and typical property ranges—such as HTV tensile 5‑12 MPa, LSR elongation 300‑900 %, tear strength 15‑50 kN/m, and Shore A hardness 20‑80—design teams can avoid over‑specification or premature failure. Whether designing a high‑pressure seal, a flexible keypad, or a biocompatible implant, aligning material properties with functional demands is essential. For expert guidance on material selection, validation testing, or custom compounding tailored to your mechanical property targets, Contact Our Engineering Team. Explore our full range of HTV, LSR, and specialty silicone rubbers at Silicone Rubber Products to find a solution backed by ASTM/ISO‑certified performance data.

Quick Reference: Test Methods and Typical VMQ Values

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Silicone Rubber Biocompatibility for Medical Devices: USP Class VI and ISO 10993 Explained

When designing medical devices, ensuring biocompatibility is paramount to guarantee patient safety and regulatory compliance. Silicone rubber has emerged as the go-to material for many medical applications due to its excellent biocompatibility. This article delves into why silicone rubber is preferred, the standards that govern its use—USP Class VI and ISO 10993—and the critical factors like extractables, leachables, and sterilization compatibility that engineers must consider.

Why Silicone Rubber Is the Default Biocompatible Elastomer

Silicone rubber has become the default choice for medical device manufacturers seeking biocompatible materials for several reasons. Firstly, its chemical structure, composed of silicon-oxygen backbones with organic groups attached, results in a highly stable and inert material. This inertness minimizes the risk of adverse reactions when in contact with human tissue or bodily fluids. Secondly, silicone rubber exhibits exceptional durability and flexibility, making it suitable for a wide range of medical applications, from catheters and implants to seals and gaskets.

Moreover, silicone rubber’s ability to withstand various sterilization methods without degrading further cements its position as the material of choice. Whether it’s autoclaving, ethylene oxide (EtO) sterilization, or radiation, silicone rubber maintains its integrity, ensuring long-term performance and reliability. For OEMs and procurement specialists, sourcing high-quality silicone rubber is crucial. Companies like Silicone Rubber Products—such as Newsil, a trusted silicone rubber manufacturer—provide validated medical-grade materials that meet stringent regulatory requirements. This ensures that the final medical devices are not only effective but also safe for patient use.

USP Class VI and ISO 10993 Test Families Explained

To ensure the biocompatibility of silicone rubber, manufacturers rely on rigorous testing standards. Two of the most prominent are USP <88> Class VI and ISO 10993. The USP Class VI standard, detailed in USP <88>, involves a series of in vivo tests that evaluate the biological reactivity of materials. These tests include acute systemic toxicity, intracutaneous reactivity, and implantation tests. The goal is to assess the material’s potential to cause adverse reactions when exposed to living tissue. USP Class VI is particularly stringent, making it a gold standard for medical device manufacturers.

ISO 10993, on the other hand, is a comprehensive series of standards that cover a broader range of biological interactions. Key sections relevant to silicone rubber include ISO 10993-5 for cytotoxicity, ISO 10993-10 for irritation and sensitization, and ISO 10993-18 for chemical characterization. Cytotoxicity testing evaluates the material’s potential to cause cell damage, while irritation and sensitization tests assess the material’s effect on skin and mucous membranes. Chemical characterization involves identifying and quantifying the chemical constituents of the material, which is crucial for understanding potential leachables and their impact on biocompatibility. Together, these tests provide a thorough evaluation of the material’s safety, ensuring that silicone rubber meets the highest standards for medical applications.

Extractables, Leachables, and Sterilization Compatibility

When assessing the biocompatibility of silicone rubber, it’s essential to consider extractables and leachables. Extractables are chemical compounds that can be extracted from the material under aggressive conditions, such as exposure to solvents or elevated temperatures. Leachables, on the other hand, are compounds that migrate from the material into the surrounding environment under normal conditions of use. Both can impact the safety and efficacy of medical devices. Therefore, manufacturers must conduct thorough chemical characterization, as outlined in ISO 10993-18, to identify and quantify these compounds.

Another critical factor is the material’s compatibility with various sterilization methods. Silicone rubber’s stability and resistance to degradation make it compatible with a wide range of sterilization techniques, including steam, ethylene oxide, and radiation. However, it’s crucial to verify that the sterilization process does not compromise the material’s properties or introduce harmful leachables. For instance, excessive exposure to radiation can sometimes lead to cross-linking or degradation, affecting the material’s performance. Therefore, OEMs and regulatory affairs specialists must carefully evaluate the sterilization process to ensure it aligns with the material’s specifications and the device’s intended use.

For procurement specialists, understanding these factors is vital when selecting a supplier. Companies like Newsil provide silicone rubber materials that have been validated for medical use, ensuring that they meet the necessary standards for biocompatibility and sterilization compatibility. This not only simplifies the procurement process but also mitigates the risk of non-compliance and potential safety issues.

Conclusion

In summary, silicone rubber’s biocompatibility, coupled with its durability and versatility, makes it an ideal choice for medical devices. Adhering to standards such as USP <88> Class VI and ISO 10993 is crucial for ensuring patient safety and regulatory compliance. By understanding the intricacies of extractables, leachables, and sterilization compatibility, OEMs and regulatory affairs specialists can make informed decisions. For further guidance, Contact Our Engineering Team to discuss your specific needs and ensure that your medical devices meet the highest standards of quality and safety.

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Silicone Rubber Post-Curing: Process, Purpose, and FDA Compliance

Post-curing, also referred to as post-vulcanization or secondary cure, is a controlled thermal treatment applied after the primary molding cycle of peroxide-cured silicone rubber. While injection-molded LSR and HTV silicone parts achieve initial cross-linking during molding, post-curing drives residual chemical reactions to completion. For OEM design engineers, procurement specialists, and material specifiers producing food-grade, medical, or aerospace components, this step directly influences extractable levels, mechanical stability, and regulatory compliance. Without a validated post-cure cycle, even a perfectly molded part can fail extractables testing or underperform in compression set.

Why Silicone Rubber Requires Post-Curing

Peroxide-cured silicone rubber systems generate decomposition byproducts, including low-molecular-weight fragments and volatile organic compounds, during the high-temperature molding process. If left unaddressed, these residuals can outgas during service life, alter tactile properties, or migrate into sensitive substrates. Post-curing elevates the part temperature to a setpoint, typically between 200°C and 250°C, for a defined dwell period, driving off these volatile byproducts and completing the cross-link density. The result is improved compression set recovery, enhanced tensile strength, and increased elongation at break.

For high-performance applications, this process transforms a marginally stable green part into a dimensionally consistent, mechanically robust component ready for demanding environments. Medical-grade implants, food-contact bakeware, and aerospace sealing systems all rely on this secondary stabilization to meet extractable limits, biocompatibility targets, and mechanical performance specifications that the primary molding step alone cannot guarantee.

Post-Curing Process Parameters

The post-cure cycle is defined by precise temperature, duration, and atmospheric control. Standard HTV silicone rubbers typically require oven temperatures ranging from 200°C to 250°C, with dwell times spanning two to eight hours depending on part geometry and formulation. Airflow patterns, whether convection, radiation, or a hybrid approach, must be uniform to prevent hot spots that could induce warpage or surface degradation. Ramp-up and cool-down rates are equally critical; rapid heating can induce internal stresses, while uncontrolled cooling may lock in residual strains.

Manufacturing facilities often choose between batch ovens, which offer flexibility for low-volume or prototype runs, and continuous conveyor systems, which optimize throughput for high-volume production. Regardless of configuration, fixtures or mandrels are used to maintain part geometry and prevent deformation during the thermal cycle. Vacuum post-curing is a specialized variant used for parts where outgassing must be minimized, such as high-vacuum chamber seals or optical lens gaskets; running the cycle below 100 mTorr accelerates volatile removal and reduces total cycle time by up to 30%.

FDA Compliance and Food-Grade Applications

For silicone components intended for food-contact or medical use, post-curing is not merely a performance enhancement but a regulatory prerequisite. FDA 21 CFR 177.2600 establishes limits on extractables leachable from rubber articles intended for repeated use in contact with food. An under-post-cured part may retain peroxides or unreacted monomers that exceed these limits, posing a compliance risk for bakeware, tubing, and gasket applications. Post-curing reduces extractable levels by ensuring complete network formation.

In medical-grade contexts, the process aligns with USP Class VI and ISO 10993 biocompatibility standards, validating that the material does not elicit systemic toxicity or hypersensitivity. Engineers must maintain documented post-cure logs, including temperature profiles and dwell times, as part of the Quality Management System (QMS) to demonstrate due diligence during FDA audits. Each batch of post-cured parts should be lot-coded and linked to the specific cure oven cycle data to enable targeted traceability if a process deviation is detected.

The process must be balanced; over-post-curing can embrittle the polymer, reducing elongation and tear strength, while under-post-curing leaves residual chemicals that jeopardize safety certifications. Silicone Rubber Products Newsil, a silicone rubber manufacturer with validated post-cure protocols, supports OEMs by providing material specifications and cure cycles tailored to specific regulatory frameworks. For procurement teams evaluating suppliers, the ability to share documented post-cure cycle data is often the deciding factor between qualified and unqualified vendors.

In summary, post-curing is a controllable, audit-ready process step, not optional finishing. By controlling chemical residuals, enhancing mechanical properties, and ensuring regulatory adherence, the post-cure cycle underpins the reliability of silicone components across the most demanding B2B applications. Contact Our Engineering Team

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Silicone Rubber Compression Set and Heat Aging: A Specifier’s Guide for Long-Term Sealing

Silicone rubber compression set measures the permanent deformation that remains after a seal is released from a compressive load, directly impacting its ability to maintain contact pressure over time. Heat aging accelerates polymer chain changes that degrade elasticity and increase set, ultimately compromising seal integrity. Specifying materials with validated low compression set and proven heat‑aging resistance reduces field failures and warranty costs for OEMs.

What Is Silicone Rubber Compression Set?

Compression set is defined per ASTM D395 (Method B), ISO 815, and JIS K 6262 as the percentage of original deflection that does not recover after a specimen is held under a specified compressive strain at elevated temperature for a set duration, then allowed to recover at room temperature. The standard test uses a Type A button specimen (29 mm diameter × 12.5 mm thickness) placed between platens with spacers to achieve a 25 % deflection, typically conditioned for 22 h at 150 °C or 175 °C, followed by a 30‑minute recovery period before measuring the final height. The result is expressed as (original thickness – recovered thickness) / (original thickness – thickness under load) × 100 %.

For seals and gaskets, a low compression set (<15‑25 %) ensures the material can sustain clamping force, maintain a leak‑tight barrier, and eliminate the need for periodic re‑tightening. Silicone grades such as VMQ (vinyl‑methyl silicone) and FVMQ (fluoro‑vinyl‑methyl silicone) generally exhibit better set resistance than generic elastomers due to the Si‑O backbone flexibility. High‑consistency rubber (HCR) formulations, especially those cured with platinum catalysts and available through Newsil’s silicone rubber products line, often yield lower set than peroxide‑cured equivalents because the platinum cure produces a cleaner, more uniform cross‑link network with fewer side‑reactions and extractables.

Test conditions strongly influence the measured value. Engineers should specify deflection percentage, exposure temperature, and recovery time exactly as the end application requires, because a 25 % compression set measured at 150 °C cannot be extrapolated to 200 °C service without additional aging data. Consistent specimen preparation and controlled post-cure are equally important for reproducible results.

How Heat Aging Changes Silicone Rubber Performance

Heat aging in polydimethylsiloxane (PDMS) primarily involves oxidation of the siloxane backbone and side‑chain methyl groups. At elevated temperatures, hydroperoxides form, leading to silanol (Si‑OH) generation and subsequent cross‑linking or chain scission. Increased cross‑link density raises hardness and modulus while reducing elongation, whereas volatile low‑molecular‑weight siloxanes can evaporate, causing shrinkage and surface tack. These processes are quantified using standards such as ASTM D573 (rubber deterioration by heat) or IEC 60216‑1 (thermal endurance indices), which track property retention versus time at temperature.

Practical consequences after prolonged exposure—e.g., 1000 h at 200 °C or 225 °C—include a measurable increase in Shore A hardness, decline in tensile strength, reduction in elongation at break, possible discoloration, and a rise in compression set as the material loses its ability to recover. Mitigation strategies involve incorporating heat‑stabilizing additives (e.g., cerium‑based or organophosphorus compounds), optimizing the vulcanization system to avoid over‑cure, applying a post‑cure to stabilize the network, and selecting a grade whose continuous service temperature rating matches the application’s thermal profile.

Specifying Compression Set and Heat Aging for OEM Seals

Request that suppliers provide full test reports: ASTM D395 compression set at the actual service temperature (or the nearest standard condition), ASTM D573 aging curves showing property retention over time, and a complete material data sheet including Shore A hardness, tensile strength, elongation at break, and tear strength. Insist on a batch‑specific certificate of analysis (COA) with traceability to the raw material lot. Validate performance on finished molded parts, not just raw sheet or gum stock, because geometry, cure cycle, and post‑mold treatment can significantly influence the final compression set and aging behavior.

Application examples illustrate the trade‑offs: engine manifold gaskets benefit from premium platinum‑cured VMQ with low compression set (<10 %) to withstand thermal cycling and fluid exposure; battery pack seals often use FVMQ for fuel resistance combined with moderate heat aging stability; HVAC flanges may accept cost‑optimized peroxide‑cured HCR where static loads and lower temperatures (<150 °C) keep compression set within acceptable limits; medical sterilization gaskets require grades validated for repeated autoclave cycles, with low extractables and minimal set after steam exposure. For further guidance on material selection and validation testing, contact our engineering team.

Compression set and heat aging are interconnected predictors of long‑term sealing performance. By specifying silicone grades with verified low compression set and documented heat‑aging resistance—such as those supported by Newsil’s validation data—OEMs reduce the likelihood of seal relaxation, leakage, and premature failure, thereby lowering total cost of ownership and field service risk.

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Heat Resistant Silicone Rubber: How to Select Compounds for 200°C to 300°C Service

When elastomers are specified for high-temperature applications, failure can occur rapidly if the material is not properly matched to the service conditions. For instance, an elastomer rated for 150°C may harden, crack, and lose sealing force within weeks when exposed to temperatures of 220°C. This guide addresses the critical challenge of selecting the right heat resistant silicone rubber compounds for continuous service in the 200°C to 300°C range. It is designed for mechanical engineers and procurement professionals sourcing elastomers for applications such as oven and appliance gaskets, turbocharger and charge-air hoses, steam sterilization seals, industrial high-temperature gaskets, and EV battery cooling loops near hot zones. By understanding continuous service temperature ratings and the factors that contribute to material degradation, you can make informed decisions to ensure long-term performance and reliability.

Service Temperature Ratings: Standard VMQ, Phenyl Silicone PVMQ, and Fluorosilicone

When selecting heat resistant silicone rubber compounds, it is crucial to understand the difference between continuous service temperature ratings and short-term peak temperatures. Continuous service ratings, which are based on extended exposure (thousands of hours), provide a more realistic indication of material performance in high-temperature environments. Here are the key silicone rubber grades and their temperature ratings:

These ratings assume air oven aging per ASTM D573. For more detailed information on silicone rubber compounds, visit our heat resistant silicone rubber compounds page.

What Actually Fails at High Temperature: Oxidation, Hardening, and Compression Set

At high temperatures, silicone rubber can degrade through two main paths: thermal oxidation and reversion. Thermal oxidation, which is dominant above approximately 200°C in air, involves the oxidation of methyl side groups. This process crosslinks the polymer network, leading to hardening, embrittlement, and surface cracking. Reversion, on the other hand, is dominant in confined hot air or steam-poor environments and involves chain scission, which results in softening and tackiness. Both degradation paths compromise the sealing force of the material.

To measure the effects of high-temperature exposure, compression set at temperature (ASTM D395 Method B) and heat aging retention (ASTM D573) are critical metrics. For example, a good silicone rubber compound should have a compression set of ≤30-50% after 22 hours at 175°C and should retain at least 70% of its tensile strength and 60% of its elongation after 70 hours at 225°C in an air oven. The table below provides typical values for these properties:

Additionally, the thermal gravimetric analysis (TGA) onset of degradation is approximately 350°C in nitrogen. For more on the properties and test standards for high-temperature seals, visit our how to choose the right silicone rubber material page.

Compounding for Heat Resistance: Stabilizers, Cure Systems, and Processing

To enhance the heat resistance of silicone rubber, several strategies can be employed:

1. Confirm the real continuous service temperature and medium (hot air, steam, oil, or ozone-rich air each require different approaches).
2. Add 1-3 phr red iron oxide (Fe2O3) as the classic heat stabilizer (or cerium hydroxide for platinum-cured compounds) to scavenge radicals and delay hardening.
3. Choose PVMQ when service exceeds 220-250°C or low-temperature flexibility below -60°C is also required.
4. Select the appropriate cure system: peroxide DBPH (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) for thick sections and platinum-cure-compatible stabilizers for addition-cured LSR.
5. Avoid acidic fillers and sulfur contamination that poison platinum cure and accelerate aging.
6. Post-cure for 4 hours at 200°C to drive off volatiles and stabilize crosslink density.
7. Validate each lot by ASTM D573/D865 aging plus compression set at the actual service temperature.

For more on compounding for heat resistance, visit our how to choose the right silicone rubber material page.

Key Properties and Test Standards to Specify for High-Temperature Seals

When specifying high-temperature seals, several key properties and test standards should be considered. These include hardness, tensile strength, elongation at break, tear strength, compression set, heat aging, continuous service temperature, brittleness point, TGA degradation onset, specific gravity, and ozone resistance. The table below provides typical specifications for these properties:

Excellent ozone resistance (no cracking at 50 pphm) is also a key property for high-temperature seals.

Selecting the right heat resistant silicone rubber compound is crucial for ensuring the longevity and reliability of your high-temperature applications. For further assistance, please Contact Our Engineering Team.

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Silicone Rubber Shore A Hardness Selection Guide

Choosing the wrong Shore A hardness for a silicone rubber part is one of the most common causes of field failure. A seal that is too soft extrudes under pressure, leaks at low compression, and tears during installation. A part that is too hard loses elasticity, develops high compression set, and cracks at low temperatures. For engineers, OEM designers, and procurement specialists who specify silicone rubber seals, gaskets, and molded components, Shore A is the single most referenced property on a data sheet and the most misunderstood. It will help you read the number correctly, match it to mechanical performance, and select the right range for your application.

Shore A Hardness Basics and How Silicone Rubber Is Measured

Shore A hardness measures the indentation depth of a truncated cone under a defined spring force, following ASTM D2240 or ISO 7619. The scale runs from 0 (gel-like) to 100 (rigid plastic). Most commercial silicone rubber parts fall between 10 Shore A (squeezable gel) and 80 Shore A (semi-rigid). Liquid Silicone Rubber (LSR) is typically molded between 20 and 70 Shore A, while High Consistency Silicone Rubber (HCR or HTV) covers a wider range from 10 to 85 Shore A. Higher numbers mean stiffer material, lower numbers mean softer and more flexible.

When you compare data sheets, always check three things: the standard (ASTM D2240 vs ISO 7619), the dwell time (typically 1 s, 3 s, or 5 s, and softer readings drop with longer dwell), and the sample thickness (a 6 mm plaque gives different values than a 2 mm part). Newsil reports Shore A on molded plaques at 3 s, 6 mm thickness, per ASTM D2240, to keep values comparable across product lines.

How Shore A Hardness Affects Mechanical Properties

Hardness is a proxy for crosslink density, and almost every mechanical property shifts with it. As Shore A increases, tensile strength and tear resistance generally rise, while elongation and compression set recover improve. Understanding the trade-offs prevents over-specifying (paying for tear strength you do not use) and under-specifying (a soft 30 Shore A that extrudes at 10 bar). The table below summarizes typical values for a general-purpose platinum-cured silicone; specialty grades (high-tear, low-modulus, low-compression-set) can shift these numbers by 10–20%.

Use this rule of thumb when reading the table: 20–30 Shore A for soft, conformable, low-pressure seals and vibration pads; 40–50 Shore A for general static gaskets and food-contact closures where balance matters; 50–60 Shore A for dynamic seals with moderate pressure (up to ~10 bar) and for molded keypads that need tactile feel without bottoming out; 60–80 Shore A for static load-bearing and structural elements. Compression set typically improves up to ~60 Shore A, then plateaus or worsens at very high hardness because stiff networks relax less on a percentage basis but start to crack under repeated deflection.

Selection Guide: Matching Hardness to Application

The fastest way to narrow your choice is to start from the working environment and work backward to the Shore A value. Below is a four-step workflow used by Newsil applications engineers, followed by recommended ranges for the most common part types we supply.

1. Define the function: static seal, dynamic seal, cushion/damper, or structural element.
2. Quantify the operating pressure, compression ratio, temperature range, and any chemical or sterilization exposure.
3. Set the compression ratio target (typically 15–25% for static gaskets, 10–15% for dynamic O-rings).
4. Select a Shore A range, then validate with a prototype compression set and leak test.

If you are unsure, start in the middle of the recommended range. For instance, a food-contact bottle closure usually feels right at 50 Shore A: soft enough to seal a slightly warped finish, firm enough to survive thousands of opening cycles. A medical fluid seal for a syringe pump plunger often sits at 40 Shore A, where compression set under 22 hr / 150 °C is still under 15% and the part can be sterilized by autoclave to 134 °C without losing elasticity.

Conclusion and Next Step

Shore A is the starting point of every silicone rubber specification, not the end of it. Match the hardness to the function (static, dynamic, dampening, structural), respect the compression ratio limits of your groove design, and always validate with a prototype test that mimics the real pressure and temperature cycle. Newsil supplies LSR and HCR silicone rubber compounds from 10 to 85 Shore A, with full ASTM D2240, tensile, elongation, tear, and compression set data on every data sheet. Send your drawing, application details, and target hardness range to our technical team and we will return a material recommendation, prototype samples, and a quotation within two business days.

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• Optically Clear LSR: Equivalent Grades, Light Transmission and LIM Molding Guide
• HTV Silicone Rubber Compounding and Mixing Process: Two-Roll Mill Procedure and Batch QC
• Low-Volatility, Oil-Bleeding-Free LSR for Automotive and Medical Parts
• Silicone Rubber Compounds for Industrial Applications

Silicone Foam vs EPDM Foam: Properties, Applications, and Selection Guide

Selecting the ideal foam material for your project hinges on a clear understanding of the differences between silicone foam and EPDM foam. This article delivers an in-depth comparison of these two materials, emphasizing their distinct properties, prevalent applications, and offering a detailed guide to facilitate your decision-making process.

Essential Aspects of Silicone Foam

Silicone foam is celebrated for its superior resistance to high temperatures and its exceptional compression set characteristics. It is a preferred option across multiple sectors due to its resilience and versatility. Below is a comparative table showcasing key attributes of silicone foam.

EPDM Foam: Key Features

EPDM (Ethylene Propylene Diene Monomer) foam is lauded for its outstanding weather resistance and cost-efficiency. This segment uncovers EPDM foam’s attributes and standard applications through a comparative table.

Choosing the Right Foam: Silicone or EPDM?

Opting between silicone foam and EPDM foam necessitates a thoughtful evaluation of several aspects. Consider these steps to ensure a well-informed choice:

1. Ascertain the temperature range of your application.
2. Assess the significance of compression set for your project.
3. Consider the environmental factors and exposure conditions.
4. Balance the cost against performance requirements.

In summary, both silicone foam and EPDM foam possess their own distinctive advantages and uses. By recognizing the differences in their properties and utilizing our selection guide, you can make a well-informed decision that aligns perfectly with your project’s requirements.

Should you require further information or assistance in selecting the appropriate foam material, reach out to us today.

Related Line: Delve deeper into silicone rubber properties and understand their role in its wide-ranging applications.

Flame-Retardant HTV Silicone Rubber: Properties, Applications and Selection Guide

Specifying a silicone material that meets UL94 V-0 flame retardancy without losing elasticity, tear strength, or processability is a real engineering challenge. Many off-the-shelf compounds pass the vertical burn test but fail elongation at break, or they require exotic curing systems that complicate existing production lines. This guide breaks down the chemistry, the measurable property ranges, the typical end uses, and the processing rules that determine whether a flame-retardant HTV silicone rubber compound will survive both the flame test and your real-world assembly. It is written for design engineers, component buyers, and quality managers working on UL94 V-0 certified silicone seals, gaskets, and wire & cable jackets.

What Makes HTV Silicone Rubber Flame-Retardant?

High Temperature Vulcanizing (HTV) silicone rubber is inherently heat-stable due to its Si-O-Si backbone, but it is not inherently flame-retardant. To reach the strict UL94 V-0 vertical burn rating, formulators add mineral or chemical flame-retardant additives that interrupt combustion through endothermic decomposition, char formation, or gas-phase radical scavenging. The table below summarizes the most common additive systems used in silicone rubber compounds for flame-retardant grades.

Because these additives are inert mineral fillers, they do not change the silicone cure chemistry, which means standard peroxide or platinum cure packages continue to work. The trade-off is mechanical performance: every additional 10 phr of filler shifts the hardness upward and reduces ultimate elongation. For gasket and seal designs that still need flexibility, loadings above 70 phr usually require a softer base polymer or a plasticizer. For a deeper look at how compounding decisions affect final part quality, see our article on food-grade HTV silicone rubber compounding principles.

Key Properties of Flame-Retardant HTV Silicone Rubber

Once a compound is flame-rated, the next gate is mechanical performance. Buyers usually start with the datasheet, but the numbers below represent realistic ranges for commercial V-0 grades and can be used as a quick acceptance filter before requesting samples.

ATH loadings of 50–60 phr are the most common route to UL94 V-0, but they can pull tensile strength toward the lower end of the 3–10 MPa window and elongation down to roughly 100%. If your application requires elongation above 250% (for example, large-format silicone rubber gaskets with deep compression profiles), request a low-filler variant or a phosphorous/nitrogen synergist system from your supplier. Always ask for lot-level test reports rather than relying solely on datasheet averages, because mineral fillers can shift cure behavior batch to batch.

Applications and Selection Considerations

Flame-retardant HTV silicone is specified wherever a rubbery seal, jacket, or profile must survive both high heat and direct flame exposure. The most common end uses are listed in the table below, along with the reason HTV silicone is preferred over alternative polymers such as EPDM, PVC, or TPE.

When selecting a compound for any of these uses, run through this minimum checklist: (1) verify UL94 V-0 certification on an actual test report, not a marketing claim; (2) confirm mechanical properties (hardness, tensile, elongation, tear) at the final part thickness; (3) match the processing method to your equipment — extrusion for continuous profiles, compression or injection molding for discrete seals; (4) confirm compatibility with any adhesives, primers, or overmolded substrates; and (5) check regulatory coverage beyond UL94, such as IEC 60695-11-10, GB/T 2408, or CSTB, depending on your target market.

Processing and Curing Guidelines

Flame-retardant HTV compounds run on standard silicone equipment, but the high filler loadings demand tighter process control than unfilled grades. Follow the steps below to keep both the flame rating and the mechanical performance within spec.

1. Compounding: Mix base polymer, flame-retardant fillers (ATH, MDH, or synergists), and additives on a two-roll mill or internal mixer. Ensure filler dispersion is uniform — poor dispersion creates weak points that lower tear strength and can cause inconsistent burn performance.
2. Shaping: Form the compound by extrusion (cable jackets, profiles, tubes) or by compression / injection molding (gaskets, sealing components). Extrusion grades need lower viscosity; molding grades can accept higher filler loading.
3. Curing: Vulcanize using a peroxide cure system (e.g., dicumyl peroxide) or a platinum addition-cure system, depending on the formulation. Peroxide systems tolerate higher filler loadings; platinum systems give lower compression set and cleaner byproducts.
4. Post-cure: Run a secondary oven cure (typically 200 °C for 4 hours, or a ramped schedule) to drive off residual volatiles, peroxides, and oligomers. Post-curing is often required to pass UL94 V-0 cleanly and to meet low-smoke specifications.
5. Inspection: Verify flame rating on production parts at the thinnest wall section, not just on lab plaques. Check Shore A, tensile, and elongation on cured specimens, and audit filler dispersion on a cut cross-section under magnification.

One advantage of HTV systems is that color pigments can be added without compromising the flame rating when used at low loading. This makes it practical to produce flame-retardant seals in safety-orange, red, or gray for visual identification in wiring harnesses and enclosures.

Choosing the Right Flame-Retardant HTV Silicone for Your Application

Flame-retardant HTV silicone rubber gives you the rare combination of rubber-like flexibility, high-temperature endurance, and UL94 V-0 flame performance — but only when the filler system, cure chemistry, and post-cure are matched to the part geometry and the end-use environment. Start by confirming the V-0 certification on the actual part thickness, then validate tensile, elongation, and tear strength against your design limits, and finish with a small production trial on your existing extrusion or molding line. If you need help selecting a grade or troubleshooting an existing UL94 V-0 silicone part, get in touch with our technical team for material recommendations and processing support.

Related Reading

• Food-Grade HTV Silicone Rubber: Compound Requirements and Certifications
• Silicone Rubber Gaskets: Material Selection and Design Guide
• HTV Silicone Rubber Compounding and Mixing Process: Two-Roll Mill Procedure and Batch QC
• Silicone Rubber Post-Curing Process: HTV Post-Cure/Secondary Cure/FDA Food-Grade
• Silicone Rubber Compounds for Industrial Applications