I was able to zip around the track today for nearly an hour with the temps around 20 degrees. Gripping my hand warmers, I was able to brave the cold and winds and get my heart rate up without suffering frozen phalanges! Wonderful! Thank you LLBean!
Hand warmers are worth the weight when it comes to winter camping. However, when temperatures are extreme, they do take about 30 minutes to heat up. "Extreme" would be temps in the teens or below. I have used them in subzero temperatures and they're fabulous.