What I find scary is that there is now a bag being sold as 'Potato Express' that is polyester. The Bed Bath and Beyond web site has three reviews that say it doesn't work well, but it looks like so far no ones has caught fire.
I am one of those that used an 'all cotton' bag that, while it did not actually catch fire, did get scorched.
I would not be surprised to learn that 'Warm Tater' had been discontinued as a liability issue. I am sure the company doesn't want to get sued, if someone house burns down, because they were microwaving potatoes in a bag made with their product.