No Sweat
Nylon and polyester do not absorb water, and because your sweat cannot evaporate they can be unpleasant to wear. This is why nylon feels clammy. Sheets made from 100% cotton, linen or even silk (should you be so lucky) are more comfortable than nylon sheets because your sweat is absorbed by the fabric, and then evaporates. It is this absorbency which makes viscose so comfortable to wear.