foam rubber vs caoutchouc

foam rubber and caoutchouc both are nouns.

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

As nouns, caoutchouc is a hypernym of foam rubber; that is, caoutchouc 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
caoutchouc: an elastic material obtained from the latex sap of trees (especially trees of the genera Hevea and Ficus) that can be vulcanized and finished into a variety of products

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

foam rubber (noun)	caoutchouc (noun)
spongy rubber; made by introducing air bubbles before vulcanization and used for cushioning or upholstery	an elastic material obtained from the latex sap of trees (especially trees of the genera Hevea and Ficus) that can be vulcanized and finished into a variety of products