The humble t-shirt is probably the hardest-working piece in your wardrobe, and that makes it one of the most important places to make a sustainable choice. The problem is that every brand claims to be "eco-friendly" and very few give you the data to back it up. We scored these five women's t-shirts using the Fashion Sustainability Index, our methodology that evaluates materials across carbon footprint, water use, pollution, chemical impact and biodegradability, then factors i