Warm feet with risk of overheating

The sock is put to the test in a climate chamber with a temperature of -10°C Photo: PZT
Breathability is analyzed by measuring water vapor absorption Photo: PZT
30,000 revolutions of abrasion is performed on samples from the sock heel and foot pad Photo: PZT
The temperature is measured with a thermal camera Photo: PZT
Then the abrasion is checked and how wear-resistant the sock is Photo: PZT

Testfakta's laboratory test of electrically heated socks shows significant differences in both price, quality, and performance. Some even become so hot that, if you're not careful, you run the risk of burning yourself. However, the test also demonstrates that it's possible to find a good sock at a reasonable price.

Peter Willebrand Published: 29 Jan, 2024

This year's harsh winter serves as a reminder of how important it is to protect oneself from the cold. In the media, we receive tips on early signs of frostbite, ranging from white nose tips to sore toes. Electrically heated socks are a welcome innovation for those who have to sit still for hours during a hunting trip or embark on long ski tours.

The basic construction of the electrically heated sock relies on embedded heating wires powered by batteries. The battery can keep the feet warm for several hours before being recharged.

The temperature is regulated either on the battery holder or via a mobile app. The maximum temperature should typically only be used for a few minutes just before heading out into the cold. On some brands, the temperature also rises very quickly to an uncomfortably high level, with a risk of burning if not careful.

Testfakta has had eight brands of electrically heated socks tested at the independent laboratory PZT in Wilhelmshaven, Germany. Prices range from 499 to 3,499 SEK.


The heat capacity, or the ability to keep the foot warm in colder temperatures, naturally carries the most weight. In the test, the effectiveness of the sock in maintaining foot warmth at a temperature of -10°C is measured. The best socks managed to slow down the temperature drop by 12-13°C over an hour, compared to a temperature drop of over 20°C for the worst-performing sock.

There is no doubt that an electric sock makes a significant difference compared to the traditional wool sock, emphasizes test leader Thorsten Kutzner at the PZT laboratory.

– All electric socks in the test make the foot significantly warmer. Then it's always difficult to assess the contributing effect of increased blood circulation that occurs when the body is in motion.

Many Swedes have experienced long periods of severe cold this winter, with temperatures clearly below the -10°C in the test's climate chamber.

– Yes, and it would be interesting to conduct an extended practical test showing how heat is distributed in the foot under real stresses. One can suspect that socks with only one heating wire then have difficulty distributing the heat evenly, says Thorsten Kutzner.

To evaluate the durability of the socks, samples from the heel and ball of the foot were subjected to 30,000 rounds of abrasion. A demanding and revealing test where several of the socks took a beating. The most resistant to wear was the sock from Seger, which also received the second-highest overall rating in the test.

All socks endured three machine washes without problems, but it is important to emphasize that the socks must be air-dried and not tumble-dried - as it can damage the heating wires.

Breathability of the socks is important for comfort, but if the boots or shoes do not breathe, it may not matter as much. Another aspect of comfort is compression, i.e., how tightly they fit around the calves. Here, there were significant differences between the different brands, making it important to try on the sock before purchasing to ensure it feels good.

So what conclusions can be drawn from our test - which sock should one choose? It naturally depends a lot on how they will be used, believes Thorsten Kutzner.

– For the elk hunter who will sit still on watch, heat retention is the most important parameter, while for the skier, it may be more important to have the ability to regulate the temperature and for the sock to breathe well.

Some models showed very high maximum temperatures, should there be clearer warnings?

– One of the models is at a critical level. At the same time, the manufacturer emphasizes clearly that one should only use maximum power for a few minutes precisely to avoid burning oneself, says Thorsten Kutzner.

Overall, Alpenheat achieved the best results in our test. The test's most expensive sock from Therm-Ic did not receive a much higher overall rating than the cheapest from INF - which took last place.

About the test

Testfakta's news agency has, on behalf of Nordic media, had the laboratory test a selection of electrically heated socks. The tests were carried out by the independent laboratory PZT in Germany. The test included the main parameters of heat capacity, breathability, battery capacity, compression, abrasion resistance, and durability in washing.

The following socks have been tested:

  • Therm-ic - Ultra Warm Comfort Socks
  • Seger – Seger Heat Mid
  • Lenz – Heat Sock 4.1 Toe Cap
  • Avignon – 1416 Heat Surround Toe 
  • Alpenheat – Fire Wool Sock
  • INF- Batteriuppvärmda strumpor
  • Zalea – Driven by heat
  • Hotronic – Heat Socks XLP 1P Surround comfort

Heat capacity
In the first stage, the sock's ability to heat various areas of the foot is measured. The foot is heated with the sock set to maximum power, and measurements are made with a thermal camera on the outside, underside, and top of the foot. For each area, the average temperature and maximum temperature within the measurement area are noted.

To test and evaluate the sock's ability to keep the foot warm for a longer period in colder conditions, the sock is placed on a foot filled with aluminum granules. The foot is heated for five minutes at maximum power. Immediately afterward, a shoe is put on the foot, which is placed in a climate chamber with a temperature of -10°C. The sock is set to medium-high power (second-highest setting), and sensors in the aluminum granules register the temperature drop over 60 minutes.

The sock's ability to release water vapor (moisture similar to foot sweat) is measured according to standard method EN ISO 14268.

The sock is placed on a medical dummy. The pressure against the dummy's calf is measured at circumferences of 23 and 36 cm. The higher the pressure, the better compression the sock provides.

Abrasion resistance
Specimens from the sock's heel and ball of the foot are subjected to 30,000 rounds of abrasion according to standard method EN ISO 12947-2. After abrasion is completed, the wear on the specimens is noted.

Impact of washing
The sock is placed in a laundry bag and washed three times in a washing machine at 30 degrees. After drying (air drying), the impact on the textiles and any impact on the sock's function are assessed.

Battery capacity
Battery capacity is measured for the right and left sock at the medium-high power setting (second-highest setting). Before measurement, the batteries are fully charged and discharged completely twice.

Interpretation and grading
The results of the laboratory test are interpreted and graded in consultation with the performing laboratory. Grading is done on a scale from 1 to 10, where 10 is best. Ratings below 6 are given only if the results are considered poor or significantly worse than other products in the test.

In the overall rating, the test's sub-elements were given the following weights:

  • Heat capacity 40%
  • Battery capacity 20%
  • Quality & durability 25%
  • Breathability 10%
  • Compression 5%