Häago Hand Warmers use a natural chemical reaction to keep your hands toasty when the frost nips and nibbles outside.

When exposed to oxygen, the hand warmers take just 5 minutes to reach up to 50°C and will stay warm for 8-10 hours. They work best if you stuff them in a pocket or under your gloves - handy if you’ve got some fiddly rope work, or just for getting into your packed lunch!

The hand warmers work by exploiting the heat given off when iron oxidises to produce iron oxide (rust!). Salt works as a catalyst to speed this process up, charcoal disperses the heat and vermiculite insulates to keep the warmth in the bag.

And because it uses natural ingredients, you can recycle the hand warmers afterwards! Nice one.