These are an excellent option to keep your toes warm in the winter if you have poor circulation like me. They cost a bit more than the chemical warmers, but quickly become more economical since you can use them over and over. Unlike chemical warmers they keep working even when your footwear is basically airtight like many well-insulated boots.Runtime can also be as long as you want since you can switch batteries, but I get about 3 hrs on one set of batteries. They also take standard AA (including rechargeable) so you don't have to purchase expensive battery packs like some alternatives.They are best used in an already warm piece of footwear though. They don't get super hot, but I find them to be the perfect temp for helping with poor circulation on cold winter days.