Could the stillsuits worn by the Fremen of Dune actually work? Stillsuit

Ever since I first read Dune, when I was much younger, I have wondered about the efficacy of these stillsuits. A person sweats, the sweat evaporates, cooling the person. The suit then condenses the sweat and recycles it after filtration to be available to drink.

The purpose of sweating is that the evaporated water vapor takes away excess body heat. The problem, as I see it, is that during condensation the water releases its heat back into the suit. The suit still has to get rid of that heat. These suits are black, or at least very dark, which makes them efficient radiators of heat, unfortunately this also makes them very efficient absorbers of heat, and as the climate of Dune is that of an extremely hot and sunny desert it seems that they would absorb much more heat than they can radiate. There does not appear to be any other mechanism to remove heat such as radiator fins on the back.
I can see that they would work very well at night to conserve water, as in desert climates the temperature drops dramatically sometimes below freezing, but the air is still extremely dry.

In my opinion people wearing stillsuits on Dune would soon be baked. Is there any possibility that such a suit could work?

Apologies to Dune fans.

  • $\begingroup$ there is some exotic technology involved ... from what I can remember, the book states that urine and feces are also processed by the stillsuit $\endgroup$
    – jsotola
    Mar 7 at 17:39
  • $\begingroup$ @jsotola Oops, forgot about the possibility of exotic technology, but still need to dump the heat somewhere. Basic thermodynamics. Luckily, we do have biological techniques to recycle human waste today. You can take a Valentine's Day tour In New York City [link] (nyc.gov/html/dep/html/press_releases/…) $\endgroup$
    – Rich
    Mar 7 at 20:22
  • 1
    $\begingroup$ @Rich Based on existing understanding of physics, you would need a power source ala refrigeration, and the result would be the suit itself or some part of it is hotter than the surrounding air. The smaller the heatsinking area the hotter it would be. $\endgroup$
    – DKNguyen
    Mar 7 at 20:45
  • $\begingroup$ @rich Also, technically, the visible colour of a material is not necessarily representative of its behaviour in long IR. They are different wavelengths after all. With exotic tech, it might be possible to have a material that is highly reflective in long IR and other dominant wavelengths of the local star, but just happens to be dark in the visible spectrum. Just be glad it's not transparent to visible wavelengths. $\endgroup$
    – DKNguyen
    Mar 7 at 20:47
  • $\begingroup$ fwiw, solar irradiance, at least on this planet, comes in visible and SWIR. (It goes back out at smth like 10nm due to blackbody). So a visibly black suit would get hot en.wikipedia.org/wiki/Solar_irradiance#/media/… $\endgroup$
    – Pete W
    Mar 7 at 21:07

4 Answers 4


Agreed. If the suit worked with high efficiency, i.e. returned most of the water to liquid form, then it would defeat the cooling effect of sweat.

So you would have to simultaneously need active cooling function in the suit. Can't remember if the suits had an energy input in the book, but you'd need energy to do cooling, for thermodynamic reasons.

Whereas the water management could, I believe, be done passively with structured micromaterials, but would then leave the cooling problem.

  • 2
    $\begingroup$ It's been a long time but I believe the only kind of energy input described in the book is that walking / moving drives the pumping and processing of liquids and waste. $\endgroup$ Mar 8 at 8:46

I am of the opinion that there is no way to get stillsuits as described in the book. The laws of physics don't leave any room for that.

(An alternative to stillsuits would have been biological adaptation. Either through selective pressure, or through some eugenics: that the desert adapted people no longer have sweat glands. Comparison: there are desert predators that live without access to water, and they are hunting prey in the day time.)

I assume that Frank Herbert came up with the idea of stillsuits to emphasize how extreme of an environment the planet is. That is, I regard it as an artistic decision. Presumably Frank Herbert made no attempt to ascertain whether the laws of physics allow for such a thing.

The thing with stillsuits does not stand on its own; in the books engineering is very far away. None of the protagonists works in any engineering capacity; none of the protagonists ever even talks to someone working in an engineering capacity.

I assume that is an artistic decision. The Dune universe is psychological, philosophical, mythological.

My assessment: to have engineering play a part in the story, that is not the kind of book that Frank Herbert wanted to write.

In my opinion the Dune books are primarily an exploration of inner, psychological world.

  • $\begingroup$ @Pete W Agree with you there. According to the link I put up "Motions of the body, especially breathing and some osmotic action provide the pumping force" as far as I can tell there are no powered functions in the suit. Fremen did have advanced technology in the book and in the movies. The design of the suit would require that. $\endgroup$
    – Rich
    Mar 8 at 0:08
  • $\begingroup$ The ultimate example of this is that he literally writes away computational devices and replaces them with mentats. $\endgroup$
    – DKNguyen
    Mar 8 at 0:35
  • $\begingroup$ @DKNguyen I suppose it could be possible that they developed a coating that reflects externally impinging long IR whilst still allowing the long IR that's internally generated to radiate out. Might work. $\endgroup$
    – Rich
    Mar 8 at 2:40
  • $\begingroup$ @Rich Or it looks black not because it is absorbing light, but re-routing the light to shine through...uhhh...the soles of their feet? $\endgroup$
    – DKNguyen
    Mar 8 at 5:47
  • $\begingroup$ @DKNguyen Herbert was definitely anti AI 60 years ago. Didn't like the idea of people giving their thinking over to machines. If we stop using our brains they're going to go the way of our tails. $\endgroup$
    – Rich
    Mar 9 at 21:16

Sideways related to the stillsuit question: in recent years a new technological solution has been developed towards passive cooling of structures that are in direct sunlight.

For passive cooling even the highest reflectivity white is not enough; as the surface heats up it the heat influx gets radiated in infrared, heating the air. (Air is for the most part of the IR spectrum not transparent to IR.) The air is heated up, and the hot air contributes to heating the surface.

There is, however, a particular window of IR spectrum that air does not interact with. That is: air is transparent to it. That is between 8 and 13 micrometer wavelength.

The following has been achieved in proof of concept form: a material that emits specifically within that window of IR spectrum. In a dry, cloudless environment that IR radiation is hardly absorbed by the atmosphere.

First proof-of-concept instances were achieved around 2014. Article on the Scientific American website (2020) titled The Supercool Materials That Send Heat to Space

Of course, any wavelength that is readily emitted is as readily absorbed. As I understand it: only a small part of the incoming light is within that window of the IR spectrum. Air being transparent to the 8-13 micrometer IR allows passive rejection of heat.


Research suggests that temperature differences could exceed 10 °C in hot, dry places.

See also:
Passive daytime radiative cooling

  • $\begingroup$ On the subject of Stillsuits, your answer, Cleonis. makes sense, 18F make a huge difference. No power needed. $\endgroup$
    – Rich
    Mar 9 at 21:28

Based on the time-honored engineering principles of over-simplification, approximation and general fudging, I have come to the conclusion that stillsuits could actually work. Kindly point out corrections or criticisms.

Let insolation be $1kWm^{-2}$ and the exposed area of human body $2m^2$. Emissivity = .97 at MIR wavelengths.

If we assume that heat input from insolation occurs on half the body and all of that heat is absorbed, that’s 1kW input. Here we ignore the fact that some parts of the body face each other and are not directly exposed to the sun and some of the sunlight is reflected, but assume that this balances out heat input from reflected light off the surrounding desert. According to John Rennie human body heat output is 120w, and according to this study this does not change between sedentary and active lifestyles link However, this is an average over the whole day, so let’s assume that during peak activity it’s up to 200w.
That means there’s a total of 1.2kW of heat that needs to be disposed of. Thanks to Cleonis we know that wavelengths of between 8 and 13 micrometers are not absorbed by air, so are radiated directly into space, where the ambient temperature is 3K and that there is a material that can accomplish this.
Human body temperature is to be maintained at 34C which corresponds to a peak black body wavelength of about 8 micrometers, just at the edge of this window.
Then from this calculator GSU provided by Georgia State U we find that total radiated energy is 1kW for $2m^2$ body area. It should not be difficult to increase the surface area of the stillsuit, for example by dimpling it, or by application of some suitable microfiber to $2.5m^2$ and we find that we are now radiating 1.2kW of heat directly into space (don’t forget, we have already accounted for incoming radiation). Ergo stillsuit works!


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