Puffy

A puffy is a lightweight, insulated jacket or vest filled with down or synthetic insulation that provides warmth while remaining highly compressible. The name comes from its puffy appearance when the insulation lofts up to trap warm air. Puffies are essential layering pieces for hikers and backpackers, serving as both active insulation during cool conditions and as a warm layer when stopped or in camp, and they pack down small to save space in a backpack.