Layering: A principle applied to dressing properly for the outdoors by wearing or packing at least three layers of clothing: an inner layer that can wick the moisture from sweat away from your body; a middle layer of insulating material for warmth; and an outer layer of a breathable and water resistant fabric.
Loft: The thickness of a sleeping bag's insulation when it is unrolled and allowed to decompress.
Lycra: A type of synthetic fibre offering very good stretch and recovery.