In a sense, every piece of clothing uses air to keep you warm: fleece, or wool, or down feathers trap air, and keep your body-generated heat from escaping into the nasty cold outside world. But NuDown's jackets want to take that a step further, giving you an inflatable jacket that's basically like wearing an air mattress.
NuDown's tech is pretty simple: in place of a conventional insulation material, their clothing has a airtight layer, that can be inflated up to the desired level using a hand-pump, or a canister of argon gas for increased insulation. The science behind it is well-proven: a thick layer of air is a potent insulator against the outside world, and the physics behind it is what keeps everything from down jackets to loft insulation working well.
But the actual practicalities may prove to be a little different. At this stage, the only real advantage of NuDown is the adjustability, which lets you tailor your jacket to the exact level of insulation you want at any one moment. But on the other hand, the NuDown jackets are heavier, more expensive, and probably more prone to getting a puncture than conventional down or synthetic insulation.