Dress in layers which are versatile, thermally efficient and space-efficient. By clothing in layers, a climber can add or remove pieces of clothing to adapt to changing weather, activity level, and body temperature. Scientifically, it is warmer to wear multiple thinner layers than an equal thickness single layer because the air between layers provides insulation. Furthermore, it takes up less space in your backpack or duffel to have thinner layers and a thick one.