Mike Kitchens - principle scientist - ADL

The primary function of an elastomeric seal is to maintain the separation of material phases. In general, seals prevent the exit (leaking) of material from a particular system. In addition to preventing leakage they also prevent the introduction of foreign material contaminants into the same system. 

Elastomeric seals can be broadly segmented into two primary categories -static seals and dynamic seals.  While the basic purpose of each is the same, the design and function can be quite different. As the name suggests, static seals are not exposed to movement while dynamic seals experience a variety of types of movement.