Sorry, forget to get to this. Here's the way I explain it in my book:
<b>Insulative cookery</b>
Also known as “haybox cooking”, insulative cookery works on the principles of insulation and retained heat. Food is put into a pot with snug fitting lid and brought to a boil. After it’s boiled from five to fifteen minutes the pot is immediately placed into a thick nest of insulative material with more insulation placed over the top. The insulation deters heat loss and the retained heat cooks the food. Insulative cookery works quite well and I have done it many times. Using this method it is possible to burn fuel (which may be scarce) for only a few minutes and use the heat created in that short time to cook food over a period of several hours to overnight. It lends itself to being used with whatever expedient materials may be at hand. I’ve done or seen it done with materials such as dry loose hay, newspapers, blankets, leaves, clothing, cardboard, styrofoam sheeting, and packing pellets. Other materials will also come to mind.
Another common form of this cooking method is to use Thermos bottles or jugs. The jugs are preheated with boiling water, then emptied. The food to be cooked is placed inside and an appropriate amount of boiling water is poured in. The jug is sealed and the food cooks from the retained heat.
To make your own haybox cooker you’ll need a pot of at least a half-gallon capacity. A smaller pot can be used, but the amount of thermal mass it is able to hold may not retain enough heat. The lid should fit snugly to retain the heated water vapor and minimize spillage. The box itself can be most anything from a heavy cardboard box, a purpose built wood box, or a styrfoam/plastic cooler. It should be of a large enough internal capacity to contain at least three or four inches of insulation on all sides of the pot, especially the top. I’ve seen a quite nice cooker made using styrofoam sheeting inside of a styrofoam cooler and another one that used spray insulation inside of a wood box.
To use your insulative cooker you should first take those steps that will minimize cooking times such as pre-soaking grains or beans, and cutting meats and vegetables into smaller pieces. Place the food in the pot with an appropriate amount of liquid and bring to a boil. Grains and tough meats should be boiled briskly for about five minutes until the pot and its contents have been thoroughly heated. Whole beans should be boiled for ten to fifteen minutes. Precisely how long you’ll have to leave it in the box depends on the amount of thermal mass you started with, how much cooking that particular food requires and the amount/quality of the insulation you used. In other words, you’ll have to experiment a bit until you get a feel for it. This method works best with those foods that use a fair amount of water and are boiled such as stews, soups, chili, rice and grains cooked in a similar fashion, pot roasts, etc.
From <b>The Prudent Pantry</b>
It's really dead simple to use and it really does work. A Google search on "haybox" will give you lots more info.
.....Alan.