Most of the cotton t-shirts shirts we print on are sourced from Bella + Canvas, and they're made with Airlume cotton. Here's a short video about what distinguishes Airlume. Along with being incredibly comfortable and durable, Airlume makes an ideal surface for vivid prints. 

Bella + Canvas is committed to being 100% sweatshop free, and they've made ecological commitments. To wit:

We are a green company through and through — taking every opportunity we can to reduce our co2 emissions. We use 7x less water than average clothing manufacturers, and our manufacturing facilities produce almost no landfill because we recycle pretty much everything.

So there you have it.