I bought this to wear while cross country skiing. It's great if you plan to get sweaty. I think I I have a slightly large head and it seems to look even larger with this hat because it's tight. I still wear it, but not because of how it looks.

I like to wear winter hats, even in then summer (but of course can only do so indoors as I live in the desert). I also like to wear winter hats on any day that it is slightly chilly. These hats are a gem. Will be using for everyday use come fall and winter. They have lovely soft material (which I would say is like a lot of yoga pants are. They are very similar to the feel and sewing of item#PAT00RF, the Patagonia Centered 3in Short). I wish it was a bit.....I guess bigger. Not because it doesn't fit my head but because I have to wear it so close to my head to get it to cover my ears like I want it to, and I prefer a cap that has a little height to it - where I can have it loose or I can synch it down over my ears. It does cover my ears completely - so please know that. It's stretchy material, and does not lose it's shape. I can't say enough. I think that this hat would keep you warm on most cold days - not sure about Everest (haven't field tested it that much), however it does provide warmth even when not doing vigorous activity. Hope this helps someone and you discover this great hat yourself!
Update 12/12/16: I forgot to update this long ago. I was unable to wear these lovely beanies that would have been warm, fit nice on my noggin, feel very soft, etc...but they were too tight :( They gave me a headache. This is of course, my own experience. I don't know if they have changed at all since I bought mine in 2015. I so want to buy one again, but am afraid it might be the same. I would not steer anyone away from this, only just give it a try and see what it's like for you, because all of the other benefits and features are brilliant and if you don't get a headache you've scored!
Update 12/26/16:
So I ordered the blue just to see if it had per chance changed style/sizing - for me, it's still too tight! :( I returned it. Just for reference I'm between 21-22" head circumference.