Made with the highest level of down available, this 900-fill down jacket provides super lightweight protection during all-out, alpine-style summit attacks. Extremely light down jacket packs a thermal punch without any of the weight, or bulk of traditional down coats. Marrying lightweight filling with Pertex® 10 denier nylon ripstop exterior, this tech-laden Summit Series® jacket provides a durable shell that’s resilient against rocks. Denier is a unit of measure for the linear mass density of fibers – the higher the denier, the thicker the fiber. Trust us when we say 10 denier is extremely svelte. This product contains at least 90% bluesign® approved fabric — a standard for environmentally responsible production.