Every fiber used in clothing costs something to make, before a single garment is even cut. The honest version of that sentence is more useful than the simplified one, because "natural is better" and "synthetic is worse" are both only partly true, and the part that is missing matters.
Cotton, and the water it drinks
Cotton uses an enormous amount of water. Widely cited research from the Water Footprint Network estimates that producing one kilogram of cotton fiber requires roughly 10,000 liters of water on average globally, counting irrigation, rainfall absorbed during growth, and the water needed to dilute pollution from processing. That figure varies significantly by region and growing method, and published estimates range considerably depending on the study, but the order of magnitude holds across most serious research: cotton is thirsty, and much of that water is drawn in places that can least afford to lose it.
Silk is not the gentle alternative
Silk is not the gentle alternative it is sometimes assumed to be. Producing raw silk is also water intensive. Estimates vary widely depending on the method, from roughly 600 liters per kilogram for some handwoven production to several thousand liters per kilogram for conventional sericulture, where most of that water goes into growing the mulberry trees that feed the silkworms. Processing raw cocoons into usable silk also takes real energy, since the cocoons need to be dried and reeled under heat, historically supplied by burning wood or by coal-powered electricity in many producing regions. Silk is, on balance, a genuinely resource-intensive fiber to produce from scratch. What it has in its favor is what happens after: as a natural protein fiber, it biodegrades, unlike the alternative below.
Polyester, and what every wash releases
Polyester flips the equation entirely. Making polyester uses comparatively little water; commonly cited estimates put it around 100 to 200 liters per kilogram of fabric, a fraction of cotton or silk. But it is made from petroleum, a non-renewable input, and it does not biodegrade in any meaningful timeframe. Worse, every wash releases microscopic plastic fibers into wastewater. A 2021 study published in PLOS One measured this directly: five domestic laundry cycles across a range of fabrics released anywhere from roughly 9 milligrams to over 1,200 milligrams of microfiber per kilogram of textile per wash, with mechanically treated polyester among the highest shedders tested. Those fibers are small enough to pass through most water treatment systems and end up in rivers and oceans, where they do not disappear. They accumulate.
So which fiber is the responsible choice?
None of them, if the question is which one to produce more of. Every fiber on this list, grown or synthesized from scratch, carries a real cost, just distributed differently: water and land for the natural fibers, permanent pollution and fossil dependency for the synthetic one. There is no version of "new" that avoids paying one of these costs.
The more useful question
Which is why the more useful question is not which fiber, but whether a new one needs to exist at all. An upcycled piece, cut from a sari that was woven decades ago, does not ask cotton or silk or anything else to be grown, spun, and dyed again. That production already happened, once, years ago, and its cost was already paid. What remains is a much smaller, more contained set of costs: the water used to wash it, the labor of cutting and resewing it into something new, none of which come close to the footprint of growing a new fiber crop.
This is not an argument that upcycling erases a garment's environmental cost entirely. Nothing does. It is an argument that reusing what already exists is one of the very few genuine ways to opt out of the biggest cost on this list altogether, the one every new garment, natural or synthetic, has no way around.
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