What's the difference between rubber and urethane bushings?

Urethane is a relatively new material invented by Doctor Bayer around 1935. Urethane bushings are commonly used in car’s suspension, steering, and wheel components to prevent sound and vibrations.

There are many discussion about rubber and urethane bushing on Internet. In my opinion, not all rubber are equal and not all urethane are equal, in general, cost decides performance.

There are many blends and formulations of urethane that can help to overcome the disadvantages of urethane that were mentioned on debate.

On the Shore hardness scale, rubber bushings ranges from 20A to 60A, while urethane has much wider range from Shore5A-98A-85D. You will find hardness of most urethane bushings on market ranges from Shore 85-95A.It is not surprising that many users tell urethane bushings are stiffer. In same hardness, urethane is not as flexible as rubber, but urethane has much wider hardness range, so it can be adjusted to lower hardness easily by manufacturer like Pepsen who make urethane prepolymer by herself, other than using plasticizers.

In terms of lifespan, economical urethane material outperforms rubber by 7-9 times on abrasion resistance, it also has much better cuts and tears than normal natural rubber. Besides, it is resistant to oil and many chemicals, reducing deterioration and degradation over time comparing to rubber. All of this results in a highly increased lifespan, lasting as long as the car does for many owners.

Even if they are all called urethane bushings, life span is much different. Based on raw material and process, there are injection molded thermoplastic urethane bushing and cast thermoset urethane bushing. The thermoplastic one is much cheaper and the performance is much lower, though tooling cost investment is much bigger.