foam rubber vs foam

foam rubber and foam both are nouns.

Word	Noun	Adjective	Verb	Adverb
foam rubber	Yes	No	No	No
foam	Yes	No	Yes	No

As nouns, foam is a hypernym of foam rubber; that is, foam is a word with a broader meaning than foam rubber:

foam rubber: spongy rubber; made by introducing air bubbles before vulcanization and used for cushioning or upholstery
foam: a lightweight material in cellular form; made by introducing gas bubbles during manufacture

Other hypernyms of foam rubber include caoutchouc, gum elastic, India rubber, natural rubber, rubber.

foam rubber (noun)	foam (noun)
spongy rubber; made by introducing air bubbles before vulcanization and used for cushioning or upholstery	a mass of small bubbles formed in or on a liquid
	a lightweight material in cellular form; made by introducing gas bubbles during manufacture

foam rubber (verb)	foam (verb)
	become bubbly or frothy or foaming