I wear this under my bike helmet in the cold weather. It's very thin so it doesn't add any bulk and my helmet still fits perfectly. Also, because it's thin it doesn't make me overheated but does give me just enough protection to take the bite out of the wind for the parts that get really cold on a bike in the winter - my ears, chin, and cheeks. I think this is perfect for under a helmet or a hat. But it's not thick/heavy enough to wear on its own.