Silk is. It's a natural fibre which can be cooling when it's hot, and warming when it's cold.

Satins made with man-made fibres are still better than cotton as, like silk, they don't pull at your hair or pull moisture out of it. However, they can be hot, and cause you to sweat.

I got mine at Dharma Trading Company. Their prices and service are terrific! Here's a link.
Peace,
Morgan

Baby Fine 3B, low porosity, normal density and elasticity
CGing since July 2008