This low-tech insulation strategy can also be applied to heating the body. In use since World War Two, electrically heated clothes have become more effective and comfortable in recent years. While their use outdoors increases energy consumption, heated clothes have the potential to save massive amounts of energy indoors.

As we wrote two years ago , insulation of the body is more energy efficient than insulation of living space. Because of its excellent insulating properties, modern thermal underclothing makes it possible to burn the heating at much lower temperatures without sacrificing comfort or sex appeal. The potential energy savings are huge, and the costs are almost nil.

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Electrically heated clothing is used by soldiers, adventurers, hunters, winter sports enthusiasts, bikers and construction workers [1]. Heated leather jackets were already used by pilots in World War Two. Bikers have used the technology for decades, using the battery of their motorbikes to supply the required energy.

The arrival of compact lithium-ion batteries has increased the performance and diversity of electrically heated clothing. There are now more types of heated clothes on the market: jackets, vests, pants, socks, underclothing, baselayers, sweaters, scarfs, shoes and gloves. Some have even become fashionable.

The energy for these garments is supplied by one or two relatively small and light batteries, hidden in a special pocket, which supply the lucky owner with some five hours of warmth. Some brands offer the possibility to plug in heated gloves or socks in a heated pants or jacket, so that they don't need a separate battery.

Carbon Fibres

Also new is the use of carbon fibres as a heating element. This material is flexible and can be inserted anywhere in the clothes without creating discomfort for the wearer. Carbon fibres are replacing embedded heating wires, which are rigid and heavy, break easily, and require more energy. Making use of low voltages for safety, electrically heated clothing comes with a button on the outside which enables the regulation of the heating system.

Unfortunately, electrically heated clothing doesn't save energy when it is used outdoors. Like most technologies that increase comfort, it increases energy consumption. The big advantage for people who work or play outdoors is that heated clothing keeps them warm during breaks in activity, when body temperature can decrease quickly.

Effective and Efficient

When used as a heating strategy indoors, however, electrically heated clothing is as sustainable as it can get. A fully heated wardrobe -- pants, socks, underclothing, shirt and vest -- has an energy output of 100 watts maximum. There's no need for the heating elements to get very hot because they remain close to the skin. An electric heater of that calibre used for space heating brings little comfort, even if it heats a very small room.

Using electrically heated clothing we could be more comfortable at even lower indoor temperatures than when using thermal clothing (which already offered heating till near-freezing conditions). Another advantage of electric clothes is that you need less volume and weight to stay comfortable. This effectiveness and efficiency of heated clothes has been confirmed by scientific research [2].

Electrically heated clothing can also be used without activating the heating elements -- the good insulation of the garments traps body heat, as with thermal clothes. In this sense, heated clothing is similar to a bicycle with an electrically assisted motor. Unlike electric cars or smartphones, the clothes don't become useless when the battery dies.

Wired or Wireless?

The only unsustainable feature of electrically heated clothing is its use of batteries. A wireless energy supply is very practical, but it would be perfectly possible to connect electrically heated clothes directly to the grid, just as you would do with your phone and laptop. It would function like an electric blanket or sleeping bag. Since many of us are sedentry, this is not as far-fetched as it may seem.

Kris De Decker (edited by Deva Lee)

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[1] Some manufacturers who sell electrically heated clothes are Gerbing, Venture Heat, Columbia, Blazewear and Milwaukee Power Tools.

[2] A Review of Technology of Personal Heating Garments, Faming Wang et al., International Journal of Occupational Safety and Ergonomics (JOSE) 2010, Vol.16, No. 3, 387-404. This study also reviews other techniques to make heated cloths, such as phase-changing materials.

The first picture shows electrically heated pants from Venture Heat. The second picture depicts a heated sock from Grabber, and the third picture a heated jacket from Blazewear. You can also make your own electrically heated clothing.

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