FirstGear's co-branded heated liners are made by Warm and Safe Heated Apparel. I had expected a replacement for the liners that came in the jacket and pants, but these are actually more universal than that. In fact, they're designed to be temperature neutral, so they can be worn all day (even when hot) flow some air when the vents are open on your jacket and pants, and when some extra warmth is needed just crank in the juice. We can't speak to their neutrality, as they were only worn in the cold, but they're made from a very soft, stretchy and comfortable material. The nice part about this is that in very cold weather, you can actually triple it up and wear your jacket liner, the heated liner and the jacket and really be toasty.