foam rubber

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A light firm spongy rubber made by beating air into latex and then curing it. Foam rubber has a wide range of uses including upholstery and insulation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Expanded latex.
• noun informal Expanded polyurethane, the padding often used in cars and furniture.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun spongy rubber; made by introducing air bubbles before vulcanization and used for cushioning or upholstery