Cold feet can make winter activities uncomfortable, especially when limited movement slows circulation. Thermal socks and insulated boots can help, but chemical warming insoles provide another option for staying warm outdoors or during long periods of standing still.
The thin, single-use insoles warm across the sole and are designed to fit inside different types of footwear without significantly changing the fit or a wearer’s stride. They begin producing heat within minutes after their individual packaging is opened, as their contents react with oxygen, and are described as providing warmth for more than eight hours.
Unlike footwear that relies on body movement to retain warmth, the insoles generate heat independently of activity. Positioned at the base of a shoe or boot, they also help limit the cold coming through the sole. Their flexible, slim construction is intended to avoid pressure points around the heel or instep—an important consideration when hiking or skiing.
Each insole is sealed separately to keep air away from its components before use, allowing unopened packs to be stored for later. The product is intended for one use, but the reaction can be paused temporarily by placing an insole in an airtight bag. To use one, put it in the footwear with the soft fabric side facing up and the smooth side down. The source notes that very tight footwear may affect how well it works.
The insoles are not battery-powered, and the source says they do not lose charge like electrical warmers. They are presented as a portable option to keep on hand for a sudden drop in temperature, including during a trip to the mountains.
Sources: El País Portada.