Sitka completely reimagined the fourth generation 90% Jacket, and in the process invented a new fabric with some incredible properties. This new iteration is three times more wind resistant than its predecessor, evening out heat retention between whisper-still mornings and howling afternoons. With the improved wind resistance, insulating the entire jacket would cause overheating, especially during periods of high exertion. So we developed a body-mapped, microgrid fleece backer that puts insulation only where you need it. The channels formed by the microgrid convectively draw warm, moist air away from the body and out of the jacket - keeping you cool on redline pushes to the next ridgetop. We improved fabric stretch and gave it a more athletic cut so you get greater freedom of movement without excess material getting in your way. The seams are thermal taped for smoothness and comfort in a variety of under layer configurations. Dual hand pockets and chest pockets help keep you organized. The 90% Jacket is pliable, durable and quiet - a precisely engineered tool that, with proper layering, can take you through 90% of your season.