This is from Checker Distributors' newsletter. They're a wholesale fabric-and-supplies dealer, so they should be "in the know":
Potato Baker Bags – A Great Make It/Take It
Jun 14th, 2010 by Penny Haren
Potato Bags have become a new on-line craze. Baking a potato in an insulated bag – in the microwave – produces a perfect baked potato in a matter of minutes. The potatoes can be cut and fluffed with a fork. The skin – which contains so many of the nutrients – stays moist and soft. Why not offer a baked potato bar at your next party – and then give them a potato bag as a gift? They are so easy, you will be making dozens for quick and easy gifts.
There is just one problem. People were making these bags with traditional cotton batting or pre-quilted fabric. Those battings have a scrim which can scorch and burn when placed in a high powered microwave. The Warm Company solved that problem by creating “Warm Tater” batting. This all natural batting does not have a scrim – so it doesn’t scorch or burn. That does not mean that you should use these bags and leave them unattended. While this product is safe, the material and thread you choose may not be – so supervision is the key!