Divers often have to wear a special warm underwear and a drysuit to feel comfortable in the winter in cold water. But even in the thickest and most expensive thermal insulator you can freeze during a long dive. Moreover thick clothes restrict movement. The best way would be to use electric heating clothing, but it is expensive and for its connection it is required to equip a drysuit with a special valve and connector. Let's save some money and make it ourselves. We made this design 5 years ago and it still works great!