t units were, they served the Ishian Zensunm's purposes A chroma-plastic outer layer turned a reflective white during die hours of sunlight, then reverted to its normal transparency at night The water which precipitated out on the cooled surface trickled down into thin ducts built into the bottom edges of the tent and was drawn into catchpockets located at the corners The process was repeated to a lesser degree on the inside lining the temperature drop earned through sufficiently to draw a percentage of the moisture lost by the inhabitant's breathing from the warmed mtenor air A small reclamation still earned with the tent served to process unne, but solid wastes were most often used as fertilizer Once the Zensunm-now called Fremen- were relocated on Arrakis in 7193, they realized that the Ishian design was primitive and inefficient The first change involved size Oa Ishia, sttlltents had most often been used as semi-permanent homes and were constructed to allow room for standing, walking, and storage An Arrakeen sblltent, on die other hand, was intended only as a temporary place of shelter for Fremen caught outside the safety of their sictch They were kept small, providing those inside with barely more space than was needed to sit fairly comfortably, to stretch out and sleep, and to store small amounts of water, sullsuit repair kits, and other items vital to desert survival The tent's shape changed with its size Rather than rising to a central peak, die new stilltents were built with a curved roof, viewed fram the end, the tent looked like a cylinder whose lower surface had been flattened where it met the ground Gone too, was the outer door-flap used in the Ishian model a sphincter-seal fashioned of clear plastic had replaced it, allowing those inside to see out while preserving the stilltent s integrity Interior flaps could be used to block off the seal and shut out unwanted light The most sinking changes, however, involved the stilltent s ability to conserve moisture The fabric making up the bulk of the tent was the same as that developed for the Fremen stillsuits, the garments which were capable of holding their wearer s mois turc loss to under a thimbleful a day Cutting through a sample of that cloth would expose numerous triumphs of microconstruction, all aimed at keeping the Arrakeen environment from snatching away precious water The layer meant to be kept on the mtenor of the tent (or, in a stillsuit, next to the skm) was porous and allowed perspiration, exhaled moisture, and the like free passage Ihe next two layers contained heat-exchange filaments so effective that a stilltent in good repair remained an average of ten degrees cooler than the outside temperature, and salt pre cipitators which kept the saline level of the reclaimed water well below the one-hundred fifty ppm mark The fourth layer trapped the water squeezed out by osmotic pressure and channeled it into the catchpocket tubes, this layer, the tubing, and the catch