These are fantastic at keeping sun and rain off your dome. They are breathable and water resistant, but can be used to cool off, if dunked in water and worn.

Some models have an interior map pocket, but stay away from them unless you have maps to keep there--the double layer of cloth retains heat, and moisture will drip down your face on a hot, muggy day.

I've seen these in all colors: olive drab, tan, Woodland Camo, sky blue and black. USGI is made of rip-stop nylon/cotton (NYCO) and are very durable. They also feature a heavy band around the top for stuffing bits of camouflaging vegetation...

Sizes are measured in inches, as per standard hat sizes, and make sure to get one that is looser than you would normally wear. This is need to accommodate shrinkage, and also to permit proper airflow around your head.

Since they've become a fashion accessory with the twenty-somethings, you can buy knock-offs just about anywhere. These are made of heavy cotton canvas, and look as though they'd absorb a lot of water, which as you may know makes the canvas WATERPROOF to RAIN as well as SWEAT! Yuck!