Silicone and polyurethane are both commonly used materials for o-rings, gaskets, seals, tubing and membranes. While both elastomers may be used to create similar products, the specific application and environment will ultimately determine whether polyurethane or silicone will be the better choice for you.
The table below summarises some of the key differences between the two materials.
|-50 °C to 80 °C||-50 °C to 230 °C|
|Very good compression set||Excellent compression set|
|Good weather resistance||Excellent weather resistance|
|Approx. tensile strength 25 MPa||Approx. tensile strength 5 MPa|
|Excellent abrasion resistance||Poor abrasion resistance|
|Not compatible with: alkalis and acids, aromatic and oxygenated solvents, brake fluids, alcohols.||Not compatible with: hydrocarbon fuels, alkalis and acids, steam over 121 °C, trichloroethylene, aromatic hydrocarbons.|
|Compatible with: most oils and fuels, cold water, salt water, metal salts.||Compatible with: oils, brake fluids, hot and cold water, salt water, high molecular weight chlorinated hydrocarbons, fire resistant hydraulic fluid, ozone.|
Both polyurethane and silicone can operate at extremely low temperatures, although silicone is the far better option in high temperature environments. Silicone can resist intermittent temperatures of up to 230°C, or up to 280°C if a heat stabiliser is added into the raw material. In contrast, polyurethane will start to degrade at 80°C which is not ideal for any high-temperature environments.
Polyurethane has an excellent tensile strength and great abrasion resistance, whereas silicone has good tensile strength, but poor abrasion resistance. For dynamic applications subject to friction and wear, polyurethane would most likely be a better option. The durability of polyurethane parts is why it is the industry standard for skateboard and forklift wheels. With this being said, silicone can be formulated to have improved tear strength, making it an ideal choice for applications such as vacuum sheeting and peristaltic pumps. Silicone also has the superior compression set, which makes it a better choice for applications requiring a long lasting, reusable seal, especially in high temperature environments.
While silicone has an excellent resistance to ozone and UV, polyurethane does not have the best resistance to ozone and UV, making silicone the more viable for most outdoor applications. However, polyurethane is resistant to most forms of fuels and oils, whereas silicone is not compatible with a lot of hydrocarbon fuels. With this in mind, polyurethane would be the superior choice for the automotive industry, although fluorosilicone compounds can be a good fuel-resistant alternative if a silicone-based material is required.
It is clear to see that there is merit in using either polyurethane and silicone, depending on what physical properties you require and the operational environment. For help selecting a material for your application, consult our applications page and contact us with any questions.