There was a company marketing a similar handwarmer several years ago. In theory, its not a bad idea. Having to boil it to recharge it is a serious fail for me. Over the years, I've tried several different handwarmer options over the years. The air activated kind work well. The charcoal stick type, at least for me, tend to burn for a few minutes and go out. I've got one of the Zippo Catalyst types to try this winter.