hard rubber vs India rubber

hard rubber and India rubber both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard rubber	Yes	No	No	No
India rubber	Yes	No	No	No

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

hard rubber: a hard nonresilient rubber formed by vulcanizing natural rubber
India 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 hard rubber include caoutchouc, gum elastic, natural rubber, rubber.

hard rubber (noun)	India rubber (noun)
a hard nonresilient rubber formed by vulcanizing 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