Silicone Products Mechanical Testing That Matters: Tear Strength, Tensile, Elongation

Silicone is prized for its softness, flexibility and durability, but these qualities depend on mechanical performance. In silicone products, tensile, tear and elongation properties directly affect safety, longevity and user comfort. For example, a poorly formulated silicone can tear unexpectedly during use, creating safety hazards (even “catastrophic consequences” in critical devices). Conversely, a high-quality silicone will stretch and rebound reliably, giving users a pleasant feel and extending product life. By testing silicone’s mechanical properties, engineers and buyers ensure the material meets design requirements. Indeed, designers aiming for “more durable, long-lasting products” rely on knowing silicone’s properties. In short, mechanical testing isn’t just a specification sheet – it’s a proxy for how the part will perform in the real world (safety, comfort and durability for the user).

Mechanical performance also underpins user experience. For example, soft-touch silicone grips are more comfortable and slip-resistant than hard plastic, but the manufacturer must verify that the softer material still has enough tear and tensile strength not to deform or fail under stress. Similarly, silicone used on overmolded buttons or handles should maintain its shape and grip through thousands of cycles. In demanding environments (temperature swings, UV, moisture), silicone’s innate resistance helps parts last longer, but mechanical tests confirm that durability. Overall, requesting and understanding silicone test data ensures the part will be safe (no unexpected rips), durable (meets lifetime expectations) and user-friendly (comfortable, reliable feel).

Key Mechanical Properties of Silicone

Silicone elastomers are characterized by three core properties: tensile strength, elongation at break, and tear strength. Understanding these terms is vital:

• Tensile Strength: The maximum stress (force per area) that silicone can withstand when stretched before breaking. In an ASTM D412 tensile test, the sample is pulled until rupture. Tensile strength (often in MPa or psi) is the ultimate stress at failure. It indicates how strong the material is under pull. (A high tensile strength means the silicone resists breaking under load; lower values mean it breaks more easily when stretched.)

• Elongation at Break: The strain or percent stretch of the silicone when it breaks. Also measured by ASTM D412, ultimate elongation is the % increase in length at rupture. Silicones typically have very high elongation (hundreds of percent) compared to plastics. For example, a silicone rated 500% elongation can stretch to 5× its original length before breaking. High elongation means the part can deform a lot, which is desirable in flexible parts (like sleeves or suction cups). Low elongation means it breaks sooner and is stiffer.

• Tear Strength: The resistance to tear propagation. In practice, a pre-cut sample (like a notched or trouser-shaped specimen) is pulled until a tear runs through it. Tear strength is reported as force per thickness (usually N/mm or kN/m). Conceptually, tear strength is the force needed to continue ripping an existing cut under tension. This matters if your silicone part can be nicked or has thin sections; a higher tear strength means small cuts won’t grow easily. (In other words, a low-tear silicone might tear completely from a small nick.)

These three properties are related but distinct. A silicone with high tensile strength may still tear easily if its tear strength is low. Elongation tells you how stretchy it is (often important for user feel). All three are critical for reliability. For context, Wacker Chemie reports typical silicone ranges of roughly 5–11 MPa tensile and 100–1100% elongation, with tear strength around 5–55 N/mm (depending on grade). Specialty high-strength silicones can reach ~10–14 MPa and 30–55 N/mm tear, whereas very soft grades might be near the low end.

Standard Test Methods (ASTM D412, D624)

To measure these properties objectively, the industry uses standard tests. The most common are ASTM D412 for tensile/elongation and ASTM D624 for tear. Both use a universal tensile tester (often called an Instron).

• ASTM D412 Tensile Test: A rectangular or “dumbbell” specimen of the silicone is gripped and pulled at a constant speed (typically ~500 mm/min) until it breaks. During the test, the machine records the stress–strain behavior. The key results are tensile strength (the peak stress) and ultimate elongation (percent strain at break). (Tests may also report modulus at 100%, 300% elongation, or tensile set, but for general use tensile strength and elongation at break are most important.) ASTM D412 essentially tells you how much force the material will take and how far it will stretch before snapping.

• ASTM D624 Tear Test: A notched piece of silicone (e.g. a crescent or “trouser” shaped specimen) is pulled apart in the tester. ASTM D624 defines several tear geometries (Type A, B, C, etc.), but a common one is a crescent cut (Die B) or trouser tear (Type T). The test records the force as the specimen tears. Tear strength is then calculated as the force per unit thickness of the sample. In other words, how much force is needed (per mm of thickness) to propagate the tear. This normalizes for sample thickness so that values (in kN/m or N/mm) are comparable. A higher result means the silicone resists tearing better. (Per ASTM D624, the tear strength is usually given in N/mm or kN/m, sometimes lbf/in.)

These tests follow strict procedures (standard specimen shape, size, speed, temperature) so results are comparable across labs. When you review a report, ensure the report cites “ASTM D412” or “ASTM D624” and notes the specimen type. For example, a lab sheet might list “Tensile Strength (ASTM D412, die C): 9.5 MPa; Elongation at break: 450%; Tear Strength (ASTM D624, die B): 28 N/mm.” These standardized numbers let you compare between materials and target values.

Interpreting Test Results: Typical Ranges

When you get test data for a silicone grade, how do you know if it’s good? First, know rough benchmarks. As one technical reference notes, general-purpose silicone rubbers usually test in the ballpark of 5–12 MPa tensile and 100–1,100% elongation. Tear strength (D624) often runs 5–55 N/mm, though most consumer-grade silicones fall mid-range. For example:

• Tensile strength: Many soft to mid-grade silicones yield ~6–8 MPa (≈900–1200 psi). The FDA-approvals spec sheet for silicone sheet rubber (40–70 Shore A) shows tensile min of 950–1100 psi (≈6.5–7.6 MPa). High-performance high-strength silicones can reach 10–14 MPa.

• Elongation at break: Soft silicones can stretch 500–800% easily. The FDA sheet lists 200–400% min for Shore 40–70A. Many formulations exceed 600–1000% for very soft grades. High-strength types often trade some stretch for strength, e.g. ~400–700%.

• Tear strength: Typical silicones often fall in the 10–30 N/mm range. The FDA sheet’s Die C values (~90–100 ppi) correspond to roughly 15–18 N/mm. Reinforced or high-strength rubbers can reach 30–50 N/mm or more (for context, specialty RTV silicones for molds are rated ~20–50 N/mm).

In practice, “good” values depend on application: a heavy-duty silicone gasket might warrant 8–10 MPa tensile, whereas a purely soft-touch grip could manage at 4–6 MPa if it deforms elastically enough. Always compare reported values against benchmarks or similar approved materials. For instance, if a supplier claims >15 MPa tensile but gives low elongation (~100%), it may be too brittle for a stretchable part. Conversely, a silicone rated 1000% elongation but only 3 MPa tensile might work for benign flex parts but not for load-bearing plugs or rings.

Factors Influencing Mechanical Performance

Silicone test results are affected by formulation and processing. Key factors include:

• Shore Hardness: Hardness correlates strongly with strength and stretch. Softer silicones (e.g. Shore A 10–30) typically have lower tensile strength but higher elongation. Harder silicones (A 50–90) often have higher modulus but may exhibit lower elongation and, in some formulations, even slightly reduced tensile strength. (Increased hardness usually comes from more filler or crosslinks, which can embrittle the rubber if overdone.) In summary: as hardness rises, expect tensile and tear to rise up to a point, but elongation to fall. Always check the combined profile: a 70A silicone may achieve 9 MPa/300% while a 30A type might be 4 MPa/800%.

• Cure System: Platinum-cure and peroxide-cure are common. Platinum-cured silicones generally yield higher tensile and elongation than peroxide-cured equivalents. (Platinum cures tend to give clearer, higher-purity elastomers with better mechanicals.) For example, one source notes platinum grades often have “better elongation, tensile, and tear strength compared to peroxide-cured” materials. However, peroxide-cured silicones may be more economical. Buyers should note which cure is used—platinum-curing is preferred in medical/adult goods for purity and strength.

• Fillers and Additives: Most silicone rubbers include reinforcing fillers (like fumed silica) to boost strength and tear resistance. Added silica typically increases tensile and tear strength, because the filler particles reinforce the polymer network. By contrast, adding too much silicone oil or plasticizer can soften the rubber—improving flexibility and cold temperature performance, but usually at the cost of lower tensile/tear. (Interestingly, some plasticizers can improve tear by making the rubber more extensible, but generally high filler = stronger rubber, while high plasticizer = weaker but softer rubber.) Pigments, cure inhibitors or other additives may also slightly shift values; always compare tested samples to the exact material you plan to use.

• Part and Specimen Geometry: Test specimens are standardized, but real parts aren’t. In tests (ASTM D624), tear strength is force normalized by thickness. In the field, thin sections and sharp corners concentrate stress and make failures easier. For example, a 2 mm wall might tear under a small nick even if a 5 mm test sample is fine. Similarly, if a component has highly non-uniform thickness or intaglio features, real-life tear resistance can differ. Designers should avoid knife-edges or sudden transitions in silicone parts. Also note that test speed and temperature affect results: faster pull rates or extreme temperatures usually change the measured values. (ASTM standards assume ~23 °C and specified speed.)

In summary, softer, less filled, platinum-cured silicone generally yields very high elongation; harder, highly filled rubber yields higher tensile/tear but less stretch. When comparing data, always consider hardness and formulation.

Guidance for Buyers: Using Test Data

When specifying or procuring silicone parts, insist on up-to-date mechanical test reports. Here are practical tips:

• Request Specific Test Reports: Always ask your supplier for ASTM D412 and D624 test results on the actual material grade you’re ordering. Generic data sheets are useful, but a lab report (with date, specimen type and conditions) is more reliable. The report should state the test standard (e.g. “ASTM D412, Die C dogbone” and “ASTM D624, Die B crescent tear”).

• Read the Lab Data Carefully: Look at both the average and the minimum (if provided). Test reports often list “Tensile Strength: X MPa; Elongation: Y%; Tear: Z N/mm”. Make sure units are correct (MPa vs psi, N/mm vs kN/m) and specimen thickness is noted. Watch for “Die C vs Die B” designations (Die C is common for tensile, Die B for tear). If multiple values (like 100%, 300% modulus), focus on ultimate tensile and elongation at break for bulk performance.

• Compare to Benchmarks: Relate the values to known targets. For example, a silicone sleeve on an adult toy might need elongation ≥300% and tear ≥20 N/mm. (By comparison, high-tear silicones for mold-making are ~20–50 N/mm.) A moderate-use gasket or ring might require only ~8 MPa tensile and ~200% elongation. If a report shows tensile of only 3 MPa, that material is very soft – possibly unsuitable for any load-bearing part. Conversely, a silicone spec’d 400% elongation but with just 2 MPa tensile is likely a very low durometer (≈10A) product – fine for plush cushions, but not for structural components.

• Consider the Application: Tailor thresholds to the product’s demands. For stretchable toys or sleeves, prioritize high elongation and good tear. E.g., a high-grade TPE (thermoplastic elastomer) or silicone intended for extreme flex might specify ≥300–500% elongation and ≥20 N/mm tear. For grips and suction bases, elongation is crucial (to form suction) – look for ≥200–300%. For rings or plungers that must bear tension, emphasize tensile strength (≥6–8 MPa) and moderate hardness (e.g. Shore 40–60A). Soft, stationary parts (like decorative toys) might only need ~5–6 MPa and ~150% stretch.

• Ask About Safety Tests: In adult or consumer goods, silicone often needs to meet FDA/medical standards (bioresistance, no harmful additives). Mechanical tests may also be part of regulatory checks (e.g. ASTM D412 results for a medical silicone). Ensure that required biocompatibility or food-grade certificates accompany the mechanical data if needed.

• Lab Accreditation: When possible, use ISO/IEC 17025 accredited labs or trusted test houses. DIY in-house tests can help screen batches, but final procurement specs should cite a reputable lab’s report for traceability.

By following these guidelines, buyers can vet silicone materials effectively. Remember: numbers don’t lie. If a report says tensile = 10 MPa for a Shore 30A rubber, that’s unusually high and worth double-checking. If a soft gel is rated only 50% elongation, it will feel hard and break easily. Use data, combined with material knowledge, to select the right grade.

Summary: Matching Tests to Applications

Note: These are illustrative guidelines. Always verify with test data and consider the product’s specific design. In general, stretchy consumer products benefit from very high elongation and strong tear resistance, whereas load-bearing or sealing parts emphasize tensile strength. For example, elastomers used in high-performance molds often have tear >30 N/mm, so domestic products with less demanding use can often accept lower (but still robust) values.

Overall, by focusing on the right test (tear vs tensile vs elongation) for each part’s function, and ensuring values meet thresholds similar to industry standards, engineers and buyers can select silicone materials that satisfy safety and performance goals.

Enrique

Hi, I am the author of this article. For the past 10 years or so, we have been dedicated to meeting the custom silicone product needs of our customers from over 50 countries and regions around the world.

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