The Patagonia Micro Puff Insulated Jacket is built around one idea: warmth that weighs almost nothing and disappears into a pack until the temperature drops. The PlumaFill synthetic fill traps heat without absorbing moisture, so it keeps working when conditions turn damp on a long approach or a ski tour. It packs down small enough to ride in the top of a pack without claiming real estate from the rest of the kit. What Our Gearhead(R) Experts Are Saying:"I stuff this into the top of my pack on every alpine start and forget it's there until the wind picks up."