Cozy, lightweight, pocket-size
Fits in a pocket for easy warmth, and thin enough to wear under a bicycle helmet--which I do most days in the winter. Not so thick that it will cause sweat to build up--this hat seems better for being active or for quick trips outside, not for something like ice-fishing or sitting at a Vikings game, where such situations probably call for something thicker.

Replacement for a lost lid
I recently lost a Smartwool Lid and was really bummed as it had become my favorite winter hat. The Lid fits my tiny head like a warm hug, can be worn under a bike helmet without any bulk or annoying seams, and is not scratchy or itchy. I was very happy to find a replacement on Altrec. The color is slightly different from the first one I owned, and has a longer fit, which is good because it covers my ears unlike the first one. I have a difficult time finding hats that fit my small head, but this one does the trick. While it was a little expensive, I didn't mind spending the money for a hat that I wear all of the time.

Hats off to you, Smartwool
I have purchased three of these hats (two black--one was misplaced--and one in brown) and I loved them all. The are thin overall as some have noted and do not block winds if they are blowing in with any sort of anger, but they definitely keep my head warm (I need all the insulation I can get) and pack down small to fit in a pocket of jacket on the trail or out and about the city. I have noticed significant differences in the cut of each hat. Two have fit on the tight side, which is a good thing for me, but one was a bit larger so it's a little sloppy on the head in places (that sounds perverted.) I find these to be my go to hats--without question. Not to mention, I got a great deal at Altrec.com. Take care, Pillow Pants

Awesome Hat
Its a thin lightweight hat, but still keeps my head warm. Its incredibly comfortable. Cotton is rotten. Smartwool rocks.

TheLid
This is exactly what I was looking for in a hat. Material on the thin side (not bulky), warm, minimal itch factor, comfortable, nice looking. I have a fairly large head and the fit is good. There is enough stretch in the material that I'm assuming it would fit someone with a smaller head equally as well. There is only one seam that runs from the top of the hat down the left side and it is nearly undetectable and there is no gathering of the fabric.