Bests & Worsts Reviews from Amazon

These require oxygen to activate so I pack them into an empty prescription pill bottle with an airtight lid when not in use. I place them inside my gloves on cold mornings for my 45 minute walk then pack them nice and tight in storage until the next morning. Each pair lasts about a week, takes about 15 minutes to heat up and needs O2 (oxygen) to produce heat. This is why these don't work well inside a winter boot. There is not enough oxygen.