NOT 100% COTTON.  I had previously ordered the Javiera Cotton 450 TC Duvet Cover by 17 Stories in Ivory and was looking for the matching bottom sheet and ordered this.  I washed them and the pillowcases before first use, and it was only after washing that I realised that this sheet is a cotton blend, and not 100% cotton like the other items I had ordered.  It's 33% polyester which is not obvious from the 500 TC description.  Since I have washed it and the polyester content is mentioned in the fine print, I can't return it so posting this just so others know before buying.