The head plays a significant role in your thermoregulation. The surface area of your head is big and it cools quickly. When in activity, this is beneficial. When you are cold, it is not. That is when our beanie comes into play. The combination of merino wool and polyester dries quickly and retains insulation properties even when wet. The beanie is stretchy, so it feels snug and is comfortable even when worn for sleeping in your sleeping bag (which is a good idea when you are getting close to the temperature limit of your sleeping bag).