I'm surprised no one mentioned bamboo sheets. I stayed at a eco friendly hotel a few times and the only thing I didn't like was the water restricted shower but that's another story. Anyway, the sheets were so soft and comfortable, they reminded me of the very old cotton sheets my dad has that are worn so soft they're fabulous. Of course I'm thinking they are high thread count cotton but I looked it up and they were bamboo. Basically, micro fiber can be polyester, however, it can be many other things. In this case, they're microfiber using bamboo cellulose. We haven't bought any sheets since I stayed there, but I will be getting some the next time we by sheets. Doing some research, they're not cheap, but we'll see if I can find a deal when I get serious.