Originally Posted by dekindy

The chemical reaction needs air which it was not getting in your boots. That is the major problem with chemical warmers. Take them out of the package in advance so they can reach maximum temperature before you put them in your boots. Better yet, put them on top of your boots over the toes so they get air and produce maximum heat. You can hold them in place with a velcro strap or oversock or shoe cover. Heatmax makes good warmers so you don't need a different brand.