No idea, and the barbers I go to is very multicultural, run by two Syrian Kurds with lots of Asian and Afro Caribbean customers. I've never heard any of them use a term to describe their hair that could be considered slang, just standard terms, curly, straight, etc.
The only slang terms I can think of come from rhyming slang. Barnet fair/ hair, syrup of figs/wig. In slang you only use the non rhyming part of the phrase, so hair would be referred to as a barnet, and a wig as a syrup.