Lately, it seems like there's really a lot of momentum behind down. And why not; unless you're out in the pouring rain, down is the warmest, lightest insulation that you're going to find. And it's all-natural, hailing from our fine, feathered friends.
Proving just how much steam down has gained lately, Outdoor Research recently introduced a down beanie. Called the Transcendent, the beanie is filled with 650-fill down and is presumably one of the warmest hats that you'll ever wear.
I tried the beanie on and it was super comfortable--just imagine a plush, down comforter wrapped around your head and you'll know what I'm saying. It also felt warm, but I was in a hot showroom floor, so I really didn't "put it to the test." My only complaint was that I felt like I couldn't hear a thing--but that's the same problem I get with my rabbit fur bomber hat, and it's small trade-off for superior warming.
The Transcendent will hit the market next fall with a very reasonable retail price of $20.
And if you're bald headed or otherwise prone to bleeding heat straight off the top, but don't need to cover your ears, Outdoor Research will also have some down caps.