The warmest fully waterproof jacket in the Arc'teryx Essentials collection. Fission Series: Insulated weatherproof outerwear | SV: Severe WFISSION SV JACKET The Fission delivers a high level of warmth with waterproof, breathable GORE-TEX protection. Designed for severe weather versatility, the thermally efficient construction pairs Coreloft™ Continuous synthetic insulation with a highly air-permeable liner to allow vapour to quickly reach the GORE-TEX membrane. This improves breathability without sacrificing warmth. The hardwearing GORE-TEX outer shuts out rain, snow and wind, and the insulated DropHood™ and collar add protection and warmth.