I use these 10-hour Heat Factory hand warmers whenever I am out in the winter outdoors for an extended period of time, like hunting, ice fishing, or skiing.  I know they have saved my fingers from frostbite many a time.  I also use a pair whenever I snowblow the driveway.  My hands get very cold when holding on to cold metal, so with a hand warmer inside my glove, my hands stay warm (instead of go numb) throughout the job.

I keep several sets of these inside my car for winter emergencies.

Upon opening the package (exposure to air), the pack slowly begins to warm.  By 15 minutes, the pack is warm and will continue to generate heat for the full 10 hours.  They do not stain hands or clothing.

konedog