Silicone rubber maintains elasticity across a -60 °C to +230 °C continuous service range, and high-temperature grades push intermittent exposure past 250 °C without embrittlement or permanent set [S1][S2]. The backbone of polydimethylsiloxane (PDMS), with silicon-oxygen bonds that rotate freely, gives the material its signature flexibility and its dominance in food-contact, medical, and outdoor sealing.
The same inert chemistry that delivers those properties also produces its two largest weaknesses: raw gum tensile strength sits in the 5-10 MPa range, and tear strength lands around 10-15 kN/m unless the compound is loaded with reinforcing fumed silica [S1]. That trade-off sets the entire selection logic covered below — silicone wins on temperature and biocompatibility, loses where mechanical abuse or hydrocarbon exposure dominates, which is why material pairs like silicone rubber versus nitrile rubber versus EPDM rubber dominate seal spec sheets.
Temperature Window and Thermal Aging Behaviour
Silicone retains useful mechanical properties from approximately -60 °C up to +230 °C in continuous service, and the industrial rubber family benchmark it against cannot match that spread on the upper end — EPDM caps near 150 °C, nitrile near 120 °C [S1][S2]. Heat-aged 70 durometer silicone compounds typically retain 80-100 % of original elongation and tensile strength after 70 h at 200 °C, the standard peroxide-cured silicone (VMQ) baseline used in oven seals, coffee machine tubing, and aerospace ducting.
Below -60 °C, the elastomer stiffens rather than cracks because its glass transition is depressed by the flexible Si-O-Si backbone; this differs from hydrocarbon rubbers, which embrittle sharply at their Tg. Above 250 °C, oxidative degradation accelerates and the part reverts to a brittle silica ash; for sustained service above 200 °C, specify a post-cured platinum (addition-cure) system and verify with a heat-age test per ASTM D573.
Chemical Resistance: Where Silicone Wins and Where It Fails
Silicone rubber resists water, ozone, UV radiation, dilute acids and bases, alcohols, vegetable oils, and polar solvents at moderate temperatures, which is why it is the default for outdoor gaskets, potable-water O-rings, and pharmaceutical tubing [S1]. Material datasheets from silicone compounders list tensile-strength retention above 80 % after 70 h immersion in 30 % sulfuric acid, 10 % sodium hydroxide, and isopropyl alcohol at room temperature.
The same inert backbone, however, swells and softens when exposed to non-polar hydrocarbons: gasoline, diesel, mineral oil, toluene, and acetone can swell silicone 20-100 % by volume depending on grade and temperature [S1]. For fuel-system seals the spec moves to nitrile rubber (NBR) or hydrogenated nitrile (HNBR), and for concentrated acids or amines, the spec moves to fluorocarbon (FKM) or perfluoroelastomer (FFKM). Silicone is also permeable to gases at roughly 10-100× the rate of butyl rubber, so vacuum seals and tyre inner-liners rarely use silicone.
Mechanical Limits: Tensile, Tear, and Compression Set
Unfilled silicone gum pulls at 5-10 MPa with 100-300 % elongation at break, and tear strength sits at 10-15 kN/m — an order of magnitude below a 60 Shore A carbon-black-reinforced natural rubber or NBR compound [S1]. Reinforcement with precipitated or fumed silica can lift tensile to 12-15 MPa and tear to 30-50 kN/m, but the cap is much lower than the 25-30 MPa achievable on a black-loaded NBR or EPDM.
Compression set on a post-cured silicone compound at 175 °C for 22 h lands around 15-25 % (ASTM D395 Method B), acceptable for static gaskets but high for dynamic O-ring duty. By comparison, an HNBR O-ring post-cured and tested to the same conditions can hit single-digit compression set. The practical conclusion: silicone belongs in static gaskets, flexible connectors, and slow-speed diaphragms; it is a poor choice for reciprocating-shaft seals and high-pressure hydraulic gland packings where extrusion and abrasion dominate.
Biocompatibility, Food Contact, and Regulatory Acceptance
Platinum-cured silicone rubber is widely accepted under FDA 21 CFR 177.2600 for repeated food contact, USP Class VI for short-term implants, and ISO 10993-5/-10 for cytotoxicity and sensitisation testing [S1]. This is the reason pharmaceutical tubing, baby-bottle teats, peristaltic-pump tubing, and medical device seals default to silicone rather than nitrile rubber or EPDM.
For process engineers specifying sanitary gaskets, the relevant test set is USP Class VI + FDA extractables + a documented post-cure cycle (typically 4 h at 200 °C) to drive off residual peroxides and oligomers. A peroxide-cured (free-radical) silicone can pass the same extractables only after the same post-cure; if the spec sheet does not state the cure system, request it before qualifying for pharmaceutical or food-plant service.
Comparison Snapshot: Silicone vs EPDM vs Nitrile on Four Spec Criteria
On temperature: silicone (-60 to +230 °C) beats EPDM (-50 to +150 °C) and nitrile (-30 to +120 °C) on the high end, and matches them on the low end within 10 °C. On hydrocarbon swell: silicone swells 20-100 % in gasoline, EPDM swells heavily in mineral oil, nitrile swells only 5-15 % — nitrile is the clear winner for petroleum media. [S5]
On weathering/UV: silicone is essentially immune to ozone and UV, EPDM is excellent (used as the reference in many weathering studies), nitrile degrades under UV without carbon-black protection. On mechanical strength: unfilled silicone (5-10 MPa tensile) is the weakest of the three; reinforced grades narrow the gap but never match the 20-30 MPa typical of carbon-black-loaded NBR or EPDM. The decision matrix reduces to: pick silicone when the limiting factor is temperature or biocompatibility; pick EPDM for steam and weathering; pick nitrile for oils and dynamic seals.
Failure Modes and Field Watch-Outs
Three failure modes account for most silicone field rejects: tear propagation under a stress concentration, compression-set loss after prolonged static compression above 150 °C, and swell softening after exposure to non-polar solvents that the part was not designed for [S1]. Each is addressable at the design stage — corner radii, gland-fill ratio, and a chemical compatibility matrix review — but is rarely fixable in service.
For new specifiers, request the compound data sheet and verify durometer (Shore A, ASTM D2240), specific gravity (ASTM D792), tensile and elongation at break (ASTM D412), tear strength (ASTM D624 Die B), compression set (ASTM D395 Method B, 22 h at 175 °C unless otherwise specified), and post-cure condition. For a true engineering comparison, weigh these numbers against the equivalent EPDM or nitrile data sheet; selecting silicone purely on its temperature window without checking compression set is a common over-spec that costs money and rarely buys performance.
Trackable signal: the silicone compounding community continues to push high-consistency rubber (HCR) and liquid silicone rubber (LSR) grades with improved tear strength, now reaching 50-60 kN/m on specialty "high-tear" formulations — a category worth re-evaluating for dynamic-seal applications that previously defaulted to EPDM. For 2026 sourcing, compare FKM total-cost numbers against silicone service-life data on the related articles below, as the upfront price gap narrows sharply once the operating-temperature envelope is factored in.
Background reading: UHMWPE Total Cost of Ownership: Resin, Processing, and Wear-Service Drivers.
