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.
(http://cache.gawkerassets.com/assets/images/4/2010/12/500x_jackethed7_01.jpg)
GizModo (http://gizmodo.com/5713615/d-is-for-design-the-anatomy-of-a-down-coat)