Asbestos was used previously but stopped for obvious reasons.
Usually the material is cut from sheets as this is one of the cheapest options. It allows manufacturers to make one complete unit tailored exactly to the specification.
Rubber is often favoured for the role as it yields slightly, an ideal feature as it allows the gasket to fill any small gaps around what it is fixed to. Rubber is also a less expensive option, but is still highly reliable and can often re-seal itself if it were to become dislodged.
However despite the material used, all gaskets have something in common - they must be strong.
They are often put under great pressure and considerable heat and as a result, most businesses will put their gaskets through the universally accepted 'hot compression test'. The results are used as a measure of how well the gasket will work.
The hot compression test determines how the gasket will perform under varying loads and temperature. It quickly became the recognised test after its development by the Klinger Group in the early 1970s, and has since been adopted by the British Standards Institution.
During the test, gaskets are subjected to temperatures of up to 450 degrees Celsius and pressures that averaged 7,250 psi through a heated hydraulic press. The results are obtained from the gasket's decrease of thickness during the test.
Once a gasket has passed the hot compression test, and the results published, it is put into production. Gaskets are often associated with the term, 'head gasket,' as this is a pivotal part of a car's engine and very often the reason for an expensive repair or trip to the scrapheap.
However, gaskets are used in a vast number of places, from the average home's kitchen and bathroom to water treatment plants, chemical plants and in the oil industry, with all of them needing different shapes, sizes and materials to match their requirements.
So when considering the strength you want and the cost you're willing to spend, it's worth remembering that rubber gaskets can often happily cover both.