Conventional materials used in today's textile industry are not sustainable. But 'natural' materials (silk, cotton, ...) and synthetic (polyester, ...) require a lot of resources to produce and then labor to make into proper clothes. 

Plus, one can't mass produce clothes or have a pre-stocked inventory as they are not one size fits all. The clothing will need to be tailored (at least) to the general physiological trends of the colony (who knows what people will look like 10 000+ years from now?).

Clothes need to be cleaned too. Some types of clothing are supposed to be thrown out regularly (e.g. underwear).

So, in a multi generational ship, what material would be optimal for clothing?