foam rubber vs natural rubber

foam rubber and natural rubber both are nouns.

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

As nouns, natural rubber is a hypernym of foam rubber; that is, natural rubber 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
natural rubber: 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, caoutchouc, gum elastic, India rubber, rubber.

foam rubber (noun)	natural rubber (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