A good layering system consists of three main layers: a base layer, a middle layer, and an outer layer. The base layer is designed to wick moisture away from your skin, often made of materials like wool or synthetic fabrics. The middle layer provides insulation, trapping heat close to your body. Fleece or down are common choices. Finally, the outer layer protects you from wind, rain, and snow, and should be waterproof and breathable.