Giro Peloton Cap
The Giro Peloton cap is a light polyester cap that performs well in warm weather, but it comes at a price.
I quite like the idea of wearing a cap under my helmet. It looks pro, for a start, and it's pretty handy for keeping the sun and rain out of your eyes. I've struggled with cotton ones - I find them too bulky, and they soak with sweat or rain pretty easily too.