I like poly thread better than cotton for crochet. After laundering the item doesn't have to be stretched that much to lay flat and it is stronger then cotton thread. I bought a lot of America's Best crochet thread which is 100% Spun Polyester when it was on clearance a few years ago for $1 a ball. I have plenty to use up in white and ecru colors. It says Bedspread weight so I'd say a size 10. Each ball is 1000 yards. I really like Knit Cro Sheen for doilys but I can't find that anymore!