Stillsuit

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A stillsuit is a body suit designed by the Fremen in Frank Herbert's world of Dune to maintain their body moisture in the harsh desert environment of the planet of Arrakis. The stillsuit's inner lining is a micro-sandwich fabric designed to dissipate body heat while drawing perspiration away from the body, filtering it, and storing the filtered water in catchpockets in the suit which can be drunk from as needed using a tube. The suit also processes moisture from the wearer's breath and body wastes. Pumps built into the heels of the suit drive the filtering mechanism.

Stillsuits would not be feasible in real life due to thermodynamic issues. Stopping the evaporation of sweat also stops its evaporative cooling effect and alternative means of heat transfer such as radiative cooling are not nearly as efficient, or, worse yet, will transfer heat in the wrong direction, from the hotter environment to the suit wearer. In daytime Arrakis this would soon result in heatstroke.^[1]

In the original novel Dune, as the planetologist Liet-Kynes is assisting Paul Atreides with the fitting of his stillsuit, he explains the suit in this manner:

"It's basically a micro-sandwich--a high-efficiency filter and heat-exchange system. The skin-contact layer's porous. Perspiration passes through it, having cooled the body . . . near-normal evaporation process. The next two layers . . . include heat exchange filaments and salt precipitators. Salt's reclaimed. Motions of the body, especially breathing and some osmotic action provide the pumping force. Reclaimed water circulates to catchpockets from which you draw it through this tube in the clip at your neck... Urine and feces are processed in the thigh pads. In the open desert, you wear this filter across your face, this tube in the nostrils with these plugs to insure a tight fit. Breathe in through the mouth filter, out through the nose tube. With a Fremen suit in good working order, you won't lose more than a thimbleful of moisture a day..."

Spoiler warning: Plot and/or ending details follow.

Use of stillsuits became practically nonexistent as Arrakis became more and more verdant under the rule of Leto II, except as cheaply made replicas. However, after his death, the sandtrout released from his body begin to undo the terraforming, returning Arrakis to its desert state and making stillsuits necessary once more.