A puffy down feather jacket is one of the lightest and warmest things you can wear. But the tradeoff is that if you get it even the slightest bit wet, you'll be wearing a cold soggy mess. Not the Brooks-Range Mojave, though; thanks to a special coating on the feathers, it doesn't skimp on the warm when it's wet.
It's light. It's flexible. It withstands frigid temperatures on top of a mountain. And in the entire history of humans staying warm, nobody's been able to beat it. Here's how you build the most powerfully simple jacket in the world.