When I first bought this cap, I was replacing a neoprene cap that I loved. It was thick, but so warm that I was worried I'd find anything as good. I love Castelli so I took a chance and ordered this. It flat blew me away.
The thing is so thin you think there is no way this can keep your head warm below 60 degrees. So, the first ride I did with it was low 60's with little wind. I had to remove it after 12 miles because I was too warm! This thing is brilliant.
It has become part of my go-to winter gear. I've ridden in low 30's and wind with this being the only thing under my helmet and it has kept me warm. It is extremely comfortable due to being so thin, and the material is super soft with an almost luxurious feel. When it warms up, I just pop the thing up over my ears and keep going.
I have yet to be anything but impressed by Castelli. Everything I own of theirs is outstanding. I highly recommend this skully cap. Again, from temps down to 30 all the way to high 50's.