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.