A method of making a composite article includes providing an elastomeric composition with a blowing agent having an activation temperature and providing at least one structural member defining a fixed gap. The composition is formed below the blowing agent's activation temperature into a solid elastomeric member approximately the thickness of or larger than the gap. The elastomeric member is assembled into the gap, which may place the elastomeric member in a state of compression in the gap. The elastomeric member is then expanded by heating it above the activation temperature. During expansion, the escape of the gas produced is limited to increase the state of compression of the elastomer in the gap by means of confining any free surfaces or by including a platy filler such as nanoclay in the composition.