When choosing garments for outdoor activities, it's more about wicking than warmth. Wicking means to pull the moisture away from your body. Choosing your base layer—the layer next to your skin—is one of the most important dressing decisions you can make before heading outdoors to recreate - especially in the winter. Everything else you're putting on after that is helping to keep you insulated. If you pick the wrong base layer, you're still going to be cold when you get wet or when you perspire.