Pressurized napalm. Napalm is jellied gasoline and when used in a flamethrower does NOT flame on exposure to the air -- there is an igniter for the steam. Napalm can be made at home from gasoline (unleaded is more environmentally friendly) by combining it with a plasticizer such as styrofoam or polystyrene beads, Joy soap (in the past, they changed for formula).