The question of which fabric is most sustainable doesn’t have a clean answer. What it has is tradeoffs—between carbon, water, land use, biodiversity, and end-of-life behavior—and the right answer depends on what you’re optimizing for and over what time horizon.
That said, the carbon dimension is where we have the most reliable data, and it’s worth going through the major fibers in some detail.
Conventional Cotton
Cotton is carbon-light relative to most synthetics in terms of fiber production. A kilogram of conventional cotton generates roughly 5–8 kg CO₂e from cradle to gate (fiber production through yarn). But this understates the picture in two ways.
First, cotton is grown with fossil-fuel-derived nitrogen fertilizers. The production of synthetic nitrogen generates substantial N₂O emissions during and after application, and N₂O has a global warming potential about 265 times that of CO₂. Fertilizer accounts for a substantial share of cotton’s real climate footprint.
Second, cotton is extraordinarily water-intensive. The Aral Sea didn’t vanish because of carbon emissions—it vanished because of cotton irrigation. Water stress and carbon are separate damage categories, and counting only carbon undersells cotton’s environmental cost in water-scarce growing regions.
Organic cotton eliminates synthetic nitrogen, which reduces direct N₂O emissions and removes the fossil fuel embedded in fertilizer production. But organic yields are typically 20–25% lower per hectare, which means more land for the same output.
Polyester
Virgin polyester sits at roughly 9–12 kg CO₂e per kilogram of fiber—higher than cotton at the fiber stage, because it’s made from petroleum. Its production is energy-intensive and it does not biodegrade at end of life.
Recycled polyester (rPET) changes the math substantially. Made primarily from post-consumer PET bottles or textile waste, rPET generates roughly 30–50% less CO₂e than virgin polyester, depending on the energy mix of the recycling process and logistics. It’s not zero—recycling is still an energy-intensive process—but it meaningfully reduces the upstream footprint.
The persistent issue with polyester, recycled or not, is microplastics. Each wash cycle sheds synthetic fibers into waterways. This is not a carbon issue, but it’s a real environmental cost that carbon accounting frameworks don’t capture.
Wool
Wool is complicated primarily because of sheep.
Ruminant animals produce methane through enteric fermentation—the fermentation that happens in their digestive systems. Methane’s 100-year global warming potential is about 27 times that of CO₂. A kilogram of raw wool generates roughly 25–35 kg CO₂e on a global average basis, making it one of the more carbon-intensive fibers by weight.
This varies significantly with grazing management. Well-managed pasture can sequester some carbon in soil, which reduces net emissions. The evidence on how much sequestration happens, and under what conditions, is contested. Regenerative grazing proponents argue the net footprint is much lower than lifecycle assessments typically show. Most LCA databases use conservative sequestration assumptions.
Wool’s counterpoint is durability and end-of-life behavior. A well-made wool garment lasts significantly longer than a cotton or synthetic equivalent, and wool is biodegradable in a way that polyester is not. Longevity is one of the most undervalued factors in garment lifecycle analysis.
Linen and Hemp
Bast fibers—linen from flax, hemp—are among the better performers on carbon in part because the plants require little irrigation, tolerate lower-input agriculture, and sequester meaningful carbon during growth.
Linen fiber production generates roughly 1.5–3 kg CO₂e per kilogram, among the lowest of common fibers. Hemp is comparable. Both are durable and biodegradable.
The constraint is scale and processing. Retting—the process that separates bast fibers—can be done with water or with enzymes, and the environmental footprint varies accordingly. Industrial capacity for hemp and linen is limited compared to cotton and synthetics, which affects both price and scalability.
Lyocell and Modal
Lyocell (sold under the brand name Tencel by Lenzing) is a semi-synthetic fiber made from wood pulp in a closed-loop solvent process. It generates roughly 1.5–3 kg CO₂e per kilogram, comparable to linen. The closed-loop chemistry means the solvent is recovered and reused, reducing both waste and water consumption.
The wood source matters. Responsibly certified forest sourcing is standard for major producers. Where it breaks down is for unlicensed producers in regions with less forestry oversight.
The Design Room Is Where This Gets Decided
The reason this analysis matters for brands is that fiber choice is a design decision, not a supply chain decision. By the time a garment reaches a pattern cutter, the material is often already specified. The carbon footprint is largely locked in.
Brands that have reduced lifecycle emissions meaningfully have done it by pushing material analysis earlier in the design process, and by giving designers carbon data alongside cost data. When a designer can see that a shift from virgin polyester to recycled polyester saves 4–6 kg CO₂e per unit, at minimal cost premium, the choice gets easier.
The harder version is fiber substitution—shifting from cotton to linen for a category where the hand-feel is different, or from virgin wool to recycled wool blends. That requires brand and consumer education, not just internal process change.
What intelligent systems can help with here is scenario modeling at design stage: given a target price point, production volume, and carbon budget, what are the viable material options? That kind of analysis exists now. Most brands aren’t using it yet.
The carbon is in the fiber. That’s where the leverage is.