Clothing has taken a bit of a battering recently because of the waste generated by throw away fashion items. Clothing can be more sustainable in a couple of ways. Firstly, polyester fibre can be generated from waste ocean bound carbonated drinks bottles. The fibre is soft and can be used as high tech wicking fabric. The usual claim is that an rPET t-shirt can be made for 6 large drinks bottles. This is particularly exciting because many recycled plastics use polymer that is reused as part of the manufacturing process. RPET generally uses polymer which post-consumer waste.
Some fabrics are natural and therefore biodegradable. Cotton as an example. Cotton however is often criticised by environmentalists because of the volume of water used in the growth of the crop and the amount of pesticides consumed. There is a standard for organic growth of cotton and you should look for products marked Global Organic Textile Standard or GOTS. For a full explanation of organic cotton have a look here: