Häago Toe Warmers use a natural chemical reaction to keep your toes toasty on frosty runs and when you're tucked up tight in your sleeping bag.

When exposed to oxygen, the Toe 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 your socks - handy for warming up the bottom of your sleeping bag.

The Toe 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.