The RidgeMonkey Ecopower USB Heated Gas Canister Cover is designed to fit all common 440-500 size butane/propane mix gas canisters. Powered by an external USB power source the heater coil gently warms the gas canister enabling you to get every last drop of fuel, even on the coldest days. The weather-resistant wipe clean neoprene outer has a zipped lower section for inserting the gas cylinder and a on/off switch.