Merino wool is miraculous. I've had some long-sleeve polo shirts and some turtleneck shirts made out of it. I can wear it outside in 30ºF, without a jacket, and I can wear it outside in 60ºF without being hot.

It not only wicks sweat away, it seems to wick the smell away. I can wear the same merino wool shirt against my skin several days in a row without it getting stinky.

And unlike some wools, it really does stand up to machine washing.