I ride wearing a silk wild rag -- a 36" square scarf -- pretty much year round. Same thing you see people wearing in cowboy movies. They're great. Just keeping the sun off the neck makes a huge difference in hot weather comfort. I do occasionally dunk them in road-side waterfalls, or pour water from a bottle over them, and they stay damp and comfortable for longer than something synthetic like a Buff.

They are available in different weights. I prefer Charmeuse in the cooler months, and Crepe de Chine in the warmer months.

The trick is to make sure you are getting one that is 100% real silk. Lots of people sell them in some silk-poly blend, and those are garbage. Expect to pay $60-$80. If it less than that, it probably isn't silk.