I purchased these in Spain years ago and haven't used them much. They can be put in the microwave to heat your hands and I suppose also in the freezer for cooling purposes. They're filled with some sort of flax or rice or something - I'm not sure as I don't speak Spanish and cannot read the instructions (pictured).
Nonsmoking home.
Reusable hand warmers (Darien (near police dept.))
This offer has been gifted to someone and is no longer available.