Your torso generates more sweat than any other body area. To keep it dry and warm (but not hot), layering is crucial. Top your base layer with a waterproof, breathable jacket. If it’s in the 30s or below, add a middle layer of fleece or wool. Then “as soon as you start to get warm, tie the top layer around your waist,” says exercise physiologist Carl Foster, Ph.D., the director of the Human Performance Laboratory at the University of Wisconsin—La Crosse.