Is fluffy a proper noun

No, the Word 'fluffy' is not a noun. The Word 'fluffy' is an adjective, a Word used to describe a noun.

The noun form of the adjective 'fluffy' is fluffiness.

The Word 'fluffy' is the adjective form of the noun fluff.

The nouns 'fluffiness' and 'fluff' are both common nouns; a general Word for a quality and a general Word for a thing.