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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?

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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
"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
@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
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
@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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