Well this bag is based on the traditional methods of Hay Box cookery.
A slow cooker, with out the electricity if you will.
Several layers of fabric are sewn together, and padded out with polystyrene beads.
Using a cooking pot, with two handles, (casserole dish that can go on the stove).
You start off your meal on the cooker top, bring the ingredients to a rolling boil for about 5 minutes. Then take off of the heat. Nestle in the Bag, close tight, by the draw string, and leave. No peaking! Leave for the required time, casseroles about 5-6 hours.
When you open it up, you have a beautifully cooked meal ready to serve.
The beauty of this is that there is no further fuel costs. No fire hazard of leaving the house with something plugged in. And if you are longer then expected it doesn't dry out, it will just gently start to cool.
There are some on sale called Wonderbags, selling for quite a considerable amount of money.