I'm not sure exactly what the lining of this vest is made of, but it must be some sort of super exotic material that fell to Earth in the lining of an alien flying saucer.  It's spooky how well it keeps you warm.  I've actually had to take this vest off outside when temps get above 50 because it gets too warm.  If you're looking for something lightweight and stylish that keeps you toasty warm this is the one to get.