Silicone is a synthetic polymer built on a backbone of silicon and oxygen atoms, combined with carbon and hydrogen. This unique structure gives the material a profile of strength that is often misunderstood, as its durability is not measured like that of steel or rigid plastics. True strength in silicone lies less in resistance to sudden force and more in its ability to resist degradation and maintain performance across extreme conditions. Understanding silicone’s strength requires examining its mechanical limits, environmental stability, and distinctive elasticity.
Defining Silicone’s Mechanical Limits
The ability of silicone to withstand a direct pulling force, known as tensile strength, is typically moderate compared to common organic rubbers. Standard grades often exhibit tensile strength between 5 and 10 Megapascals (MPa), though specialized high-strength formulations can push this value to about 15 MPa. This modest strength means silicone will generally fail under less load than materials like nitrile rubber or EPDM, which have higher ultimate breaking points.
Where silicone excels is in elongation, which measures how much a material can stretch before breaking, proving its flexibility under strain. Silicone rubber routinely demonstrates elongation percentages between 200% and 800%, meaning it can stretch two to eight times its original length before failure. This high elasticity allows the material to absorb significant energy and deformation without permanent structural damage. This property makes it an excellent choice for applications requiring repeated stretching or shock absorption.
Tear resistance is another mechanical metric where general-purpose silicone can show vulnerability, particularly once a small cut or notch is introduced. Standard silicone can be susceptible to the rapid propagation of a tear, making it a poor choice for dynamic applications involving sharp edges or abrasion. However, material scientists have developed high tear-strength grades by incorporating reinforcing fillers, such as nanosilica. These enhanced materials can achieve tear resistance values around 39 to 45 Newtons per millimeter (N/mm), representing a significant improvement over conventional silicone.
Resilience to Extreme Environments
Silicone’s most celebrated strength lies in its exceptional resistance to temperature extremes, a direct benefit of its silicon-oxygen backbone. The material retains its physical properties and flexibility across a remarkably broad thermal range, typically from -60°C to 230°C. Specialized formulations can even extend this upper limit to nearly 300°C for continuous operation. Unlike organic rubbers, which become brittle in the cold and degrade rapidly at high temperatures, silicone remains stable and functional throughout this spectrum.
The material also demonstrates outstanding durability against environmental degradation from exposure to ultraviolet (UV) light and ozone. Most organic polymers have carbon-carbon bonds that are easily broken down by UV radiation and atmospheric ozone, leading to cracking and embrittlement over time. The stronger silicon-oxygen bonds in silicone make it inherently resistant to these weathering effects, allowing it to maintain its integrity for decades in outdoor applications. This stability is why silicone is favored for exterior seals, gaskets, and building materials exposed to the elements.
Silicone exhibits good chemical stability and inertness, particularly when exposed to water, oxidation, and many common solvents, acids, and bases. This resistance prevents swelling, softening, or degradation, which is a common failure mode for other elastomers in harsh fluid environments. While it is not universally resistant to all chemicals—certain fuels and highly concentrated solvents can cause it to swell—its general chemical resilience contributes significantly to its long operational lifespan.
The Role of Flexibility and Hardness
Silicone’s operational strength is frequently defined by its hardness, which is measured using the Shore A durometer scale. This scale quantifies a material’s resistance to permanent indentation, with values ranging from 0 (very soft) to 100 (hard, rigid). Most functional silicone products, such as gaskets and seals, fall within the 25 to 80 Shore A range. A lower durometer number indicates a softer, more flexible material that conforms easily to surfaces, while a higher number signifies a stiffer material with greater resistance to abrasion.
The ability of silicone to hold a specific hardness level is one of its most important strengths in gasketing and sealing applications. It maintains this durometer reading consistently across its wide temperature range. This ensures that a seal remains soft enough to conform in freezing conditions and firm enough to resist extrusion at high heat, a unique advantage over materials that drastically change hardness with temperature fluctuations.
Another measure of strength for silicone in sealing applications is its compression set. This metric describes the permanent deformation that remains after a material has been squeezed and the pressure is released. A low compression set value indicates that the silicone will quickly return to its original shape, which is paramount for a reliable seal. Silicone typically has an excellent, low compression set, meaning it resists permanent flattening and maintains its sealing force, even after prolonged exposure to compression and heat.