The fit is snug and close to the head as a layer of magical merino that is warm when cold and cooling when warm. I've used it for mtb, walking, ski helmet and motocycle lid and it has performed perfectly. If you motocycle or ski you will know how hard it is to find a layer that you can't feel - the Keats smashes it out the park if you get your knee and elbows down. Get one, put it in your pocket and never get caught out with a cold brainpan again! Also with the neck warmer you can make the ultimate NINJA style - and in my book that makes it essential.
My new go to, goes under my helmet all the time, biking climbing whatever. Comes with me all the time.