What is the string that comes standard with a lot of YYF yoys?

Came with The Grind Machine, for example. The bright green string. Is there a specific name? Is it cotton? Poly?

Thanks in advance ~

It’s poly and probably YYF-brand string.

I heard it was YYF String. I would imagine it is a 100% poly string. I don’t prefer it myself but if you like, try asking YYF.