It can't take the place of a good set of cold winter gear, but it is adequate for a little spot of warmth when you are feeling chilly, pop into your gloves or in your boots. It need to be in an enclosed space that helps to retain heat. It can't give out that much or else users will get burns, so you need to help trap the slow heat. If you are totally outdoors and with wind biting cold temperatures, that little sachet is not gonna do ****.