A microwave potato bag might be something you've never heard of - many people haven't. It is exactly what the name would indicate: a cloth bag that is used to cook potatoes in the microwave. Let's examine why you'd want to do that.
Typically, a baked potato would be produced in the oven. The oven would be pre-heated, the potato would be washed, then pricked with a fork, and finally placed into the oven. Long after, possibly an hour or even more, the potato was ready. But who wants to wait for an entire hour? Plus, the skin can be dried out and crunchy, which may not be exactly what you want.
Instead, you could use the microwave. In this case, you'd usually follow the same wash and prick procedure, but then place the potato in the microwave instead of the oven. This of course leads to a much faster cooking time, but introduced an entirely new problem. The texture of the potato is ruined. It can be hard, solid, or chunky, and definitely doesn't give the traditional baked potato experience.
Up until recently you've been forced to choose between the convenience of the microwave and the superior results of the oven. But the microwave potato bag changes that. All you have to do is wash the potatoes as usual, place them into the bag, and then stick them in the microwave. You don't even have to use a fork to prick holes in them. The result is a perfectly fluffy potato that reproduces the long-baked oven experience with only a few minutes of waiting.
A high quality potato bag will generally be made up of three separate layers: a decorative outer shell, a plain inner lining, and a filling or batting of some sort. It should close around the potatoes when they are in the bag, sealing in the right amount of moisture for perfect cooking.