What is the plural of hairs?

The plural noun is hairs.

The noun 'hair' is an uncountable noun as a Word for a substance that grows from human or animal skin.
The noun 'hair' is a count noun as a Word for the strands or shafts of this substance.

Examples:
"Your hair is a mess!" (uncountable)
"You have cat hairs on your coat." (countable)