Gloves or mittens with friction generating area connected to thermally conductive layer within glove.
Gloves with a slightly raised/textured area on both gloves to rub together to generate friction heat. This area (or areas) would be in a location(s) where accidental fricition would be minimized, or located in a compartment where exposure of the surface would require user action. The friction causing surface would be connected to a thermally conductive layer that would heat up as a result of the friction.
Problem this idea/invention addresses:
Cold hands. Wet hands. Purchasing and disposing of temporary heat sources. Lack of alternative means (electricity, solar, etc) for generating heat.