A small team at Otherlab, which does all kinds of weird things, has been using ARPA-E funding to develop what they're calling "thermally adaptive materials." We'll call it self-poofing fabric, for its ability to dynamically change its insulation in response to temperature. The idea is that the fabric will provide a small amount of insulation when it's warm out, and then increase how insulating it is (by trapping more air) in response to colder temperatures. When you see the prototype fabric in action, it looks like magic.
What's most exciting about Otherlab's fabric is that it operates completely passively. There's no power source, no wiring, and no controls—nothing but a combination of common synthetic fibers, each of which has different thermal expansion characteristics.
It might take a minute or so for the fabric to transform itself from completely flat to completely poofed and then another minute to go back, but that's certainly quick enough to be useful. At minimum poof, the fabric insulates you about as well as a heavy T-shirt. And at maximum poof, it's equivalent to heavy outdoor gear, nearly tripling its insulating ability in response to a temperature drop of 15 °C.
Since the fabric is made of commodity materials and the manufacturing process is just like that used to produce other fabrics, the team at Otherlab (including Brent Ridley, Jean Chang, and Leah Bryson) says it should be able to scale up from fabric samples to actual garments within the next year.