I agree that the potato bags are a novelty. Each bag must be made with 100%cotton. This means that the batting, material and thread must be 100% cotton. No fillers like polyester and scrim can be involved or it will melt in the microwave/catch fire. The potato should be washed 1st and can not be poked with a fork. Wrap the potato with a wet paper towel and place in the potato bag. This has worked best for me. Since the potato bag holds the moisture in, the microwave button for potatoes no longer applies. The time for cooking is now less. I have cooked a potato in 2.5 minutes. The cooked potatoes are moist and the peel comes right off.
If you leave the potato bag in the microwave for more then 5 mins, I believe it will catch fire or melt. The potato bags or bowls are not meant for long periods of cooking in a microwave.