The Burton ak Swash Synthetic jacket maps 60g PrimaLoft Silver insulation to the chest and kidneys, warming the core without adding bulk through the arms and shoulders. A Rider Wrapped Fit with articulated patterning keeps that mobility intact, so a full GORE-TEX 2L shell and real insulation still move like a shell alone. What Our Gearhead(R) Experts Are Saying:"I noticed the difference on a hike to a sidecountry stash, reaching overhead to grab a branch without the jacket fighting me anywhere in the shoulders. My core stayed warm the whole way despite the effort, which told me the insulation was doing its job exactly where they mapped it."