O-rings are usually made of elastomers. An elastomer refers to a rubber material that can change its shape when any force is applied, and then come back to that original shape when the force is removed. In chemistry, elastomers are found as long chains of Carbon, Silicon, Hydrogen, and Oxygen atoms, having intermolecular cross-linkages to connect various chains. The cross-links in an elastomer ensure that it will come back to its original shape even after being stretched or compressed. The length, strength, and distribution of polymeric cross-links in an elastomeric material affect the substance’s precise properties.

Below is a list of common elastomers and their abbreviations: