Clothes are often made of (treated) wood fiber - it is what rayon/viscose is. [
https://en.m.wikipedia.org/wiki/Rayon]
Clothes made of ‘bamboo fiber’ are made of rayon, for example.
Cotton is also normally mercerized [https://en.m.wikipedia.org/wiki/Mercerisation], or treated like Denim, etc.
It’s all made of cellulose at the end of the day.