When weight and breathability are key, we reach for our Outdoor Research Helium AscentShell Jacket for our fast-and-light alpine pursuits. The Helium surpasses the performance of heavier hard shells by fusing two technologies-the lightweight durability of Pertex Diamand Fuse fabric and the lightweight, air permeable, and highly breathable waterproofing of a 3-layer AscentShell membrane. This makes for a light and breathable jacket that's weatherproof enough to withstand some of the planet's harshest conditions. It takes up little space in our packs while easily layering in between our mid-layers, backpacks, and harnesses for high-output activities in high mountains.