The Härkila Heat L/S T-shirt is made from 80% nylon and 20% spandex, making it quick-drying, stretchy and hardwearing. It has a modern cut, fitting relatively snugly to the body. In the parts of the upper body most vulnerable to cold – the chest, between the shoulder blades and in lumbar region – there are heating membranes sewn in which can be set to 35C, 43C or 50C using the push button on the chest. Unlike older heating technologies, the heating membranes are flexible enough to be folded up and packed away with the garment they are sewn into. The T-shirt can also be safely machine-washed. In a pocket on the right of the T-shirt is a long, fabric-covered cord with a waterproof USB plug, so you can connect a power bank of the desired capacity, which you can keep in your trouser pocket, for example. The pocket can be used to store the cord when the power bank is not connected. With a power bank of 10,000mAh, the T-shirt can output its highest temperature of 50C for about 7 hours at an outdoor temperature of 0C. To save energy, the heating membranes automatically go into standby once the jacket has reached the set temperature. They then turn back on automatically if the temperature falls 1-2 degrees below the set level. The result is that the T-shirt is heat-regulating, because the heating function automatically turns off if you get hot from intense exertion and turns back on when you are sitting or standing still. The T-shirt is supplied with a drybag to pack it away in.

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