In Dune, Fremen (and anyone else wishing to travel the desert) wear a Stillsuit, an all encompassing body suit which traps and recovers all moisture leaving the body. This includes urine, fecal moisture, breathing moisture, even menstrual fluids but primarily - sweat. It is captured, condensed, runs down to the feet and is pumped through walking action into basins where it can be drunk (again) by the suit wearer. Cool idea.

But the purpose of sweat is to cool the body; how does the body cool if the sweat is never allowed to evaporate, especially on Arrakis, a notorious desert planet?

  • 4
    Desert doesn't mean hot. It means little rain. Many regions on Arrakis are hot during the day, but they also get very cold as the sun goes down; keep out of the sun (the book's suits were white, unlike all the movies), "ration" your heat, and you'll have plenty of time to cool the apparatus down through the night. It's also noted in the books there is a rather massive flow of air from the poles towards the equator, bringing lots of cold air, so it's not clear exactly how hot the regions where the books take place are. Finally, the suits do lose water. They're just more efficient than humans.
    – Luaan
    Apr 21 '19 at 15:20
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    @Luaan No, the suits are described as 'gray' and 'slick' multiple times in the books. For example: "Paul saw the contents of the mound exposed: the pale glistening gray of a stillsuit, a battered literjon, a kerchief with a small book in its center"
    – James
    Apr 21 '19 at 22:01
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    @Luaan Also, Dune was very hot in the books. It's mentioned several times. That's part of the reason they often travel at night.
    – James
    Apr 21 '19 at 22:07

Sweat is still allowed to cool the body before it's captured by the suit.

“Certainly,” Kynes said. He felt up under the robe for the shoulder seals, speaking as he examined the suit. “It’s basically a micro-sandwich—a high-efficiency filter and heat-exchange system.” He adjusted the shoulder seals. “The skin-contact layer’s porous. Perspiration passes through it, having cooled the body… near-normal evaporation process. The next two layers…” Kynes tightened the chest fit. “… include heat exchange filaments and salt precipitators. Salt’s reclaimed.”


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    That addresses where the vapor goes, if the idea is that the suit catches vapor. But it also defeats the whole point of evaporation, since capturing vapor also captures its kinetic energy. In other words, if the vapor isn't lost, the heat isn't lost either.
    – Misha R
    Apr 21 '19 at 8:35
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    @MishaR - I didn't write the thing. Go yell at Frank Herbert('s grave).
    – Valorum
    Apr 21 '19 at 8:43
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    I am not saying that this isn't the best answer available. But not everything in sci fi is hand-waving, so it's useful to acknowledge it. As far as Dune goes, it's an answer. As far as real life goes, it isn't.
    – Misha R
    Apr 21 '19 at 8:53
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    @MishaR - The stillsuit itself relies on fantastical tech. Within minutes the suit would (IRL) be filled with dirt and grime and poop.
    – Valorum
    Apr 21 '19 at 8:55
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    @MishaR - I interpreted the reference to "heat exchange filaments" as indicating that there's some process to conduct heat to the outside of the suit.
    – Adamant
    Apr 21 '19 at 9:17

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