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Uniqlo sells HEATTECH heat-generating clothing.

Advertising claims

When HEATTECH absorbs body moisture, tiny droplets generate heat. Thermographs clearly show that HEATTECH maintains more warmth, more evenly over your body, than 100% cotton.

Is this just a marketing gimmick or does this fabric generate heat as advertise?

  • 1
    Sodium and water can generate heat, but what happens to this when you wash it? Does it get used up? Aerogel has the highest thermal insulation, but it's a solid, not fabric. Ceramic can reflect thermal radiation, but this has no ceramic. – Chloe Jan 12 '13 at 21:07
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    "HEATTECH generated more warms [...] than 100% cotton" Who the heck wears cotton when they're worried about being warm? This claim doesn't tell you anything except that they weren't able to make a favorable comparison to a good cold weather fiber like wool. – dmckee Jan 13 '13 at 0:51
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    @DVK I've done that many times with plain wool, but these days you can get so-called "super washed" wool which simply doesn't itch. You can also get silk, cashmere, or alpaca if you can afford it. This may be a good product, but that line should be laughed at, because it is trying to play the reader for a fool. – dmckee Jan 13 '13 at 17:28
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    I'm skeptical about the use of a thermograph - I think "hot" colours would indicate that it's acting as a poor insulator of body heat! – Andrew Grimm Jan 14 '13 at 8:43
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    @AndrewGrimm look carefully the guy being thermographed is holding a jacket (presumably the jacket being tested) open (the light blotches on the sides are residual heat from the body) – ratchet freak Jan 14 '13 at 22:02
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This appears to be a poor translation of the original Japanese description:

"吸水発熱"

(e.g. from http://www.uniqlo.com/jp/store/goods/408603-00, but listed on other items too)

"吸水" means to absorb moisture, and "発熱" means to generate heat but is commonly used in the context of clothing or bedding making you feel warm even though it's actually just retaining/reflecting your own body heat.

A Japanese person would not take this to mean that the clothing actually produces heat on its own, but merely that it will keep them warm.

A better translation to English for "generates" would be "retains". I can also confirm from personal experience that it works very well.

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