If you wear this in cold weather with a pair of glasses, sunglasses, or ski goggles, I can guarantee you they will fog up.  Because your warm/moist breath is not allowed to leave your face as quickly, it will go up the spaces on either side of your nose and get on your eyewear.

Also, the neck on this product is far too short; I constantly feel a breeze on my neck when I am outside.  The way to fix this is to either wear a scarf or a coat with a tall collar, but frankly, why should I have to if this product is supposed to do the trick?