Guys, a very basic query: does anyone know what is this product called glove warmer (or was it heater), I have seen it in sportshops but clueless how it works.

Thing is my fingers freeze very fast while running, although I will be sweating on the body, and this spoiling the fun of running.

I can wear thick fleece lined gloves instead, but they don't look nice on my sleek running profile not easy to store in pockets when not needed. I have tried wearing very thin gloves under a normal cycling glove, which works better, but I would still like to know of better solutions.

So what is this product. I think the wrapper said it keeps you warm for some hours, does it actually generate heat by chemical reaction or something