The Härkila thermal vest is made of a lightweight, lined fabric with elastic membranes on the sides. Inside, it has a heat-reflective lining that not only prevents heat loss, but also enhances the effect of the vest's thermal membranes. The high collar is lined with a soft fleece. In the parts of the upper body most vulnerable to the cold - between the back and the lumbar region - there are sewn-in heating membranes. Using the associated iWarm smartphone app, these heating membranes can be set to the desired temperature between 30C and 52C. The membranes can also be adjusted to 38C, 46C or 52C using the chest button, so there is no need to rely on your smartphone. Unlike older heating technologies on the market, the heating membranes in Härkila's heated vest are flexible enough to be folded and stored with the garment to which they are sewn. In addition, the vest can be safely machine washed. In the right pocket of the vest there is a waterproof USB plug, so you can connect a power bank of your choice. With a 10,000mAh battery, the vest can reach its maximum temperature of 52C for about 7 hours at an outside temperature of 0C. Once the vest has reached the set temperature, the thermal membranes automatically go into standby mode to save energy. They then automatically turn on again if the temperature drops 1-2 degrees below the level set for the vest. The result is that the vest regulates heat, as the heating membranes automatically turn off if it gets hot from exertion and turn back on when sitting or standing. The vest has an inside pocket, two side pockets and a radio pocket on the left chest, and is supplied with a dry bag for storage.