Envirofit Rocket Stove Pot Skirt Accessory G-33SKT
Basically, whenever you cook something in a pot over any stove with an open flame, you are wasting quite a bit of of heat.  You heat the bottom of the pot but a lot your heat just shoots out to the sides and is lost.  Things get even less efficient the windier it gets.  By using a pot skirt you can greatly increase your efficiency by not only heating the bottom of the pot, but also the sides.  You do this by forcing that hot air to travel very closely to the sides of the pot, about one centimeter.   Envirofit has come up with a unique design you can adapt to different pot sizes.