It's not often I get a chance to test a gadget that was designed for use in developing countries. But this one isn't just for those folks—it's got hometown uses as well.
The Wonderbag ($50) is a soft-sided insulated bag that turns almost any short-handled pot into a slow cooker. The pot needs short handles in order to fit in the bag, something like a Dutch oven or small stockpot. The idea is that you heat your pot on the stove to boiling, let it cook for five minutes so the pot and its contents are hot, then put the pot into the bag and let it rest for several hours.
In developing countries where resources for cooking and heating might be limited, this bag helps conserve those resources It also means no one needs to tend a fire and watch the food. Here, cooking with less heat is probably more about not heating up the house. For folks who don't like leaving a traditional slow cooker running unattended, this solves that problem as well. I could also imagine using this for transporting food while it's finishing cooking on the way to a potluck party.
To see how well the Wonderbag held heat in, I tested it with different foodstuffs in the pot, as well as different sized pots. I left the Wonderbag in a relatively cool location, but a warm spot would give you even more cooking time. On average, it took five hours to go from a starting temperature of just below 200°F (I live at high altitude, so the boiling point here is 202°F) down to 140°F. At sea level, you'd likely get an extra hour or more—the largest temperature drop was during the first hour, then it slowed.
Cooking in the Wonderbag takes some experimentation. A pot of dried beans cooked to perfection, while beef stew was less successful. Recipes are included, so you'll have a good idea of what works best.
Besides using the Wonderbag to cook, it would be great for keeping food warm or cold for serving, just like any insulated cooler. It's not washable in a washing machine, so if you've got a messy pot, you should put a kitchen towel inside to catch any spills. However, it can be spot cleaned to take care of any little spills and spatters, then just let it air dry.
For every Wonderbag purchased, one is sent to Africa and donated to a family that can use it. If you don't want your own Wonderbag, you can also donate without buying.
Disclaimer: Testing samples were provided to Serious Eats.