Virtually weightless and boasting the warmth of a parka, the new Lightweight Down Jac-Shirt is the ideal layer worn alone in frigid weather or under a shell when the snow starts flying. With its extremely lightweight shell and goose downs unrivaled compressibility, It packs into tight spaces so you can always take it with you.Goose down consists of large spherical clusters of the soft under-plumage of geese, each cluster with thousands of soft filaments that trap heat. This is why goose down has been the champion of lightweight warmth for centuries. There simply is no insulation that is warmer and lighter. We use only responsibly-sourced goose down, which means that the geese that provide it are treated humanelynever live-plucked or force-fed. All of Filson's goose down is traceable and certified to follow the RDS (Responsible Down Standard), and is processed in bluesign-approved facilities.The lightweight shell fabric is 2-oz. nylon thats treated for water resistance to minimize the need for rain jacket. The snap-front closure will never jam like zippers can, and can be operated easily while wearing gloves. Dual chest pockets with snap-secure flaps keep your essentials safe. Angled-entry hand pockets are lined with Filson's signature Alaskan Guide flannel for added warmth and next-to-skin comfort. Side-seam slits at the hem provide ease of motion during rigorous backcountry action.