gecho

The one's I'm using are a bit of a hack. I originally bought them as heated socks which came with 2 removable pads in each sock. The pads didn't go under the toes so I just taped them to my insoles and used them as insole heaters. This year they started disintegrating so I made a new heating pads. The heated socks were discontinued after the first year, as the wires in the battery holder had a habit of breaking loose from the switch. I fixed mine and moved the switch and batteries to a pair of Blackberry phone cases and have been using it that way for nearly 3 years now, duct tape and all. I like that the heating pads I have are wider than my boots so they wrap around the side of my toes.

You can buy similar heating pads fairly cheaply. The tricky part would be finding battery packs to attach to footwear. A battery exposed to the cold might need to be lithium polymer, some lithium ion batteries don't do well in the cold.

Any heated insole that is trim to fit, won't have any heating at the edge of the insole so that may limit their effectiveness at keeping toes warm.