These worked perfectly for a recent trip we took to Germany in the winter. With temps in the 20's and 30's and a gf who gets cold very quickly, these were perfect. Everyone we shared them with loved them as well! Funny enough, after reading the reviews here, we expected roughly 5 hours of use out of them, but we actually got close to 10 hours as advertised out of every pair. The heat output varied throughout the day, but we found they lasted longer when left alone inside an enclosed space.