The Cerium SL is the lightest Down jacket in the Arc'teryx lineup. It blends warm down insulation with Coreloft 40 and 100 synthetic insulation. The Arc'teryx Cerium SL Down Jacket is a warm, yet lightweight jacket that's great for layering. The synthetic is placed in moisture-prone zones so that sweat generated by activity doesn't cause your jacket to stop providing warmth. SL stands for super-light, making the Arc'teryx a great choice for packing. A DWR coating provides protection from light precipitation, and a trim fit makes layering under a shell or over everyday clothes easy.