Elasticity

Rubber consists of long flexible molecules that are in continuous Brownian motion at normal temperatures due to thermal agitation. As a result, the molecules take up a variety of random configurations like a basketful of snakes. When the molecules are straightened out by an applied force and released, they spring back to random shapes as fast as their thermal motion allows. This is the origin of the unique ability of rubber to undergo large elastic deformations and recover completely – rubber molecules are highly flexible and therefore highly extensible, but in the absence of an external force they adopt rather compact, random configurations.