This 15 degree bag powered by synthetic PrimaLoft Sport insulation will keep you toasty and warm on your next trip to the mountains. PrimaLoft® Sport is a premium performance insulation made from fine fibres that trap warm air in the tiny air pockets that are formed between them, mimicking the natural properties of down insulation. This results in a lightweight layer that keeps your body heat in and the cold out with minimal bulk and some water resistance.