Check the sentence below
My hair is rather short but I usually plait it/or them?
I'm confused about whether I should use the singular or plural pronoun.
Hair is both countable and uncountable Noun, but it is usually singular when it refers to all the hairs on one's head.
George has brown hair.
But if it refers to more than one hair, a few hairs, then it takes the plural form and needs a plural verb.
George has brown hair, but I found a hair on the sofa and suspect he's getting some gray hairs.
When you are talking about specific strands of hair, use the plural form.
Hair can be singular (one hair)
I found a strand of hair on your sofa. or I found a hair on your sofa
Non-countable singular (when it refers to all the hairs on one's head)
Shawn has black hair.
Or plural (three hairs, some hairs)
I Found not one, but three hairs on your sofa.
As Maulik.V said,"To make 'hair' singular, you need to quantify it. So, 'I found a strand of hair on the sofa.'"
Note that we do not say "Strands of Hairs."
You would use "it". "Hair" when used to mean hair as a material rather than to refer to an individual hair is uncountable and takes singular conjugations as well as pronouns. It is not like words like "family" where, though it is singular and takes singular conjugations, we might use plural pronouns in the same sentence because these are not uncountable, but rather collective nouns.
For example, we might say:
I love my family, but I wish they would give me more privacy.
My hair is really long; I think I need to have it cut soon.
Note that collective nouns can use singular pronouns, too, though, when thought of as a single entity.
I love my family, but it's getting too big to keep track of.
When we talk about hair on the scalp, we use 'singular'. And, that's why you have written 'My hair is...'
Thus, we'd surely continue the singular further.
My hair is rather short, but I usually plait it
Check this entry on OALD that gives us some idea about it.
Her hair was tied back in a long thick plait.