Polypro(fleece,etc...) or wool does not absorb much water ,10%(from leaks or sweat) and it will move the moisture away from your skin. If you have ever skied in cotton, you've experienced the moisture situation, I would think in a drysuit you'd start feeling clammy, especially if you are doing repetitive dives. Plus, once you're out of the water, cotton takes forever to dry. Nothing like a long drive home in damp, cold, clothes. Cotton clothing has no place in technical layering, be it for diving, skiing, climbing, etc... .In an emergency, it will let you down big time!! Sorry flannel and blue jeans guys, but that's the truth!!:bonk: