The fur is so soft.
Explanation:
* "Fur" is a collective noun and usually doesn't take a plural form.
* "So soft" is an adjective phrase describing the fur.
If you were talking about multiple pieces of fur, you could say:
* The furs are so soft.
The fur is so soft.
Explanation:
* "Fur" is a collective noun and usually doesn't take a plural form.
* "So soft" is an adjective phrase describing the fur.
If you were talking about multiple pieces of fur, you could say:
* The furs are so soft.