Makes you ready for the worst
Sufficiently thin that it fits nicely under a ski helmet. But warm enough that you can get through pretty much the worst cold out there. It has enough malleability that you move it up or down over your nose + mouth when it's really bad out, but it doesn't hang limply if you pull it down to your chin. Smartwool makes the best balaclavas & neck gaiters. A really great choice.