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.