Perfect weight cotton. Not too thin but not thick, bulky cotton either. You may want to size up if you don't wear your T-shirts on the tighter side. I wae a large or extra large in T-shirts (depending on manufacturer) and I bought these (6 different colors) in XL. They don't have super short sleeves and the sleeves aren't too tight. The only negative is the length. They are really too long for me, as I am only 5'4. If you are tall, you will probably find this a real bonus.
Rating: [4 of 5 Stars!]