The Fiber Guide: What Clothes Are Made Of,
and What Their Labels Leave Out
A practical guide to plant, animal, regenerated-cellulose, and synthetic clothing fibers, with the questions that help distinguish material names from production evidence.
Start with the tag, then follow the material
A clothing label is a useful first document, not a full origin story. In the United States, most covered textile products must identify fiber content, country of origin, and a responsible company (FTC textile-labeling guidance). A cotton label tells you what the fiber is, not the farming practice. A polyester label identifies a polymer, not whether the feedstock was newly made or recovered. Neither percentage alone tells you how a fabric was dyed, who made it, or whether a later environmental claim has been verified.
Some makers publish more. Some use independent certifications. The goal here is to help you ask consistent questions of any garment, not to pretend that every brand is silent or that one fiber name can guarantee an outcome.
The four questions
- What material is it? Read every fiber and its percentage. A small proportion of elastane can change stretch and care, and a blend can complicate sorting or recycling.
- Where did the raw material come from? For plants or animals, ask where and how they were grown or raised. For synthetics, ask what feedstock was used and what a "recycled" claim actually covers. For regenerated cellulosics, ask about pulp sourcing.
- How was the fiber turned into fabric? Spinning, chemical processing, dyeing, finishing, and cut-and-sew each raise different questions. A farm certification is not necessarily a dye-house certification.
- What evidence supports the claim? Is it a brand statement, a documented supplier practice, a product-specific independent certification, or a measured outcome? What parts of the supply chain does it cover?
A material map, without a good-versus-bad ranking
Plant-derived fibers: cotton, linen/flax, hemp
These start with crops. The farm, local water conditions, fiber preparation, dyeing, and product life all matter. "Natural" is a description of origin, not a guarantee of low impact. Organic certification is one way to substantiate particular agricultural practices: the USDA says its organic rules apply to agricultural products grown for food and fiber. A crop-level organic claim does not, by itself, describe every subsequent textile-processing step.
Ask: Is the claim tied to this product's fiber? Which standard or certifier is named? Does it cover the farm only, or also processing?
Cotton
What it is.
A natural plant fiber — single-celled seed hairs harvested from plants of the genus Gossypium. After harvest, it moves through ginning, carding, and spinning into yarn.
Questions to ask.
Is the organic claim tied to this product's fiber? Does it cover the farm only, or also processing? Where was it grown, and under what water conditions?
Claim and evidence.
USDA organic certification at the farm level verifies the crop was grown without prohibited synthetic pesticides, synthetic fertilizers, sewage sludge, or genetically engineered seeds (link). Under USDA's own textile policy memo, an "organic cotton" tag verifies the organic origin of the crop fiber — it does not by itself imply that post-harvest processing or dyeing met organic standards unless those facilities are separately certified (link). Cotton is also a relatively water-intensive crop: FAO guidance puts typical seasonal water requirements at roughly 700–1300 mm depending on climate and season length (link).
Related PWW reading.
/WaterUse · /journal/what-a-cracker-box-knows-that-a-clothing-label-doesnt
Linen / Flax
What it is.
A durable bast fiber extracted from the stem of the flax plant (Linum usitatissimum), converted to yarn through retting, scutching, and hackling.
Questions to ask.
Is the organic claim farm-level only? What can the producer tell you about retting and processing? Is durability reflected in the garment's design?
Claim and evidence.
Flax is typically grown in cool, temperate climates as a rainfed crop, with seasonal water needs around 450–650 mm — generally less irrigation than cotton under comparable conditions (links and link). As with cotton, farm-level organic certification verifies how the crop was grown, not how the fiber was processed afterward (link).
Related PWW reading.
Animal-derived fibers: wool, alpaca, silk
These begin with animals and agricultural landscapes. The relevant questions include animal care, land management, processing, durability, and traceability. A fiber's ability to last for years does not establish how it was raised or processed.
Ask: Can the producer explain the sourcing region and animal-welfare standard? Is the claim verified for the product, the supplier, or only a company-wide program?
Wool
What it is.
A natural protein fiber — primarily keratin — shorn from the fleece of sheep. Softness and next-to-skin comfort track with fiber diameter, measured in microns.
Questions to ask.
Can the producer name the sourcing region and an animal-welfare standard? What does the standard cover — and what does it leave out? Is the claim verified for this product or only a company-wide program?
Claim and evidence.
The Responsible Wool Standard (RWS), managed by Textile Exchange, prohibits mulesing, covers farm-level animal welfare, land management, and social welfare, and tracks chain of custody — but does not cover downstream wet processing, chemicals, or dyes (link). In trade classification, "superfine merino" denotes wool of about 18.5 microns and finer (industry trade standards).
Related PWW reading.
Regenerated cellulosics: viscose/rayon, modal, lyocell
These are made by processing cellulose into new fibers, often from wood pulp. The starting material and the industrial process both matter. "Plant-based" alone doesn't tell you where the pulp came from or how process chemicals were handled. For a specific product, look for traceable feedstock and meaningful information about processing, rather than inferring an entire industry's practices from one fiber name. The FTC's textile guidance is also relevant when a product marketed as bamboo is actually rayon made from bamboo.
Ask: What is the generic fiber name on the tag? What wood or plant source is documented? What evidence addresses chemical management?
Viscose / Rayon
What it is.
A regenerated-cellulose fiber: wood or plant pulp chemically dissolved and re-extruded into filament. Soft and drapeable, but the process is industrial.
Questions to ask.
What is the generic fiber name on the tag? Where did the pulp come from? What evidence covers chemical management in processing?
Claim and evidence.
FTC rules define rayon as a manufactured fiber of regenerated cellulose (link). Products made from bamboo cellulose must be labeled "rayon" or "rayon made from bamboo" — the chemical process, in the FTC's words, leaves no trace of the original plant or its natural properties in the finished fiber (link). Pulp sourcing is the key question: responsible-sourcing verification exists through FSC chain-of-custody and the CanopyStyle audit framework (link).
Related PWW reading.
Lyocell
What it is.
A close cousin of viscose defined by its direct-solvent process: wood pulp dissolved in an organic solvent, spun, and with the solvent recovered rather than discarded.
Questions to ask.
Who verifies the "closed-loop" claim for this product? Where is the pulp sourced? Does the claim cover the specific mill, or the fiber type generally?
Claim and evidence.
FTC rules define lyocell as cellulose precipitated from an organic solution with no substitution of hydroxyl groups (link). Peer-reviewed literature on commercial lyocell operations reports solvent recovery above 99.5% (link; pulp sourcing can be tracked through FSC chain-of-custody certification (link).
Related PWW reading.
Synthetic fibers: polyester, nylon, acrylic, elastane
These are manufactured polymers. They can offer performance and durability, and they also require scrutiny of feedstocks, processing, shedding, and end-of-life pathways. Recycled polyester is still polyester; a recycled-content claim does not mean a garment is plastic-free or that it cannot shed microfibers. The site's microplastics guide examines the latter question and links to its sources. A fiber blend is not automatically a mistake, but its function and tradeoffs should be explained.
Ask: Is recycled content product-specific and independently documented? Is it post-consumer bottles, textile-to-textile material, or something else? What is the garment expected to do well, and how long can it stay in use?
Polyester
What it is.
A manufactured polymer — under FTC rules, a long-chain synthetic polymer of at least 85% ester of a substituted aromatic carboxylic acid; the common garment form is polyethylene terephthalate (PET). Durable, inexpensive, and plastic.
Questions to ask.
Is recycled content product-specific and independently documented? Recovered from what — post-consumer bottles, or textile-to-textile? What is the garment expected to do well, and how long can it stay in use?
Claim and evidence.
FTC rules define the polyester family (link). A 2024 peer-reviewed study in Environmental Pollution found recycled polyester shed about 31% more microfibers than virgin polyester — 497 versus 378 fibers per gram of fabric — because recycled fibers are more brittle (link). "Recycled" answers a feedstock question; it does not answer the shedding question.
Related PWW reading.
Elastane (spandex)
What it is.
A synthetic elastomer — under FTC rules, a manufactured fiber of at least 85% segmented polyurethane. Small amounts (often 1–5%) give a garment stretch and shape recovery.
Questions to ask.
Is the stretch percentage disclosed with the blend? What happens to this garment at end of life? Is the elastane serving the fit, or hiding a fabric quality question?
Claim and evidence.
FTC rules define elastane as at least 85% segmented polyurethane (link). Even at low percentages, elastane complicates both mechanical and chemical recycling: it entangles carding machinery and interferes with the dissolution of the host fiber, so blends require energy-intensive separation steps (link). The same literature reports that most end-of-life elastane-blended garments currently cannot be processed by standard fiber-to-fiber recycling and are landfilled or incinerated (link).
Related PWW reading.
What a certification does, and doesn’t do
A certification can make a defined claim more credible, but its scope matters. USDA Organic concerns specified agricultural production and handling. GOTS says its independent certification covers requirements from organic fiber processing through the textile processing supply chain, including environmental and human-rights criteria. Those are different questions, not interchangeable seals. Check that a claim applies to the item you are holding, and what it verifies. No single logo is a complete lifetime impact score.
A practical comparison in a store
Suppose two shirts both say "100% cotton." The label makes them comparable on fiber composition. To compare production, look for a specific claim about the cotton, a named standard and certifier, product-level documentation if offered, and information on processing and labor. If one brand answers and another doesn't, you have learned something about disclosure, not necessarily the unreported impact of either shirt. Don't convert absence of documentation into a fabricated measurement.
The same test applies to a polyester jacket: compare function and expected lifetime, then examine any claim of recycled content and what material was actually recovered. "Recycled" may answer a feedstock question while leaving laundering and shedding questions open. The strongest choice is not determined by one word on the hang tag.
From food labels back to clothing
Packaged food generally comes with an ingredient list and Nutrition Facts (21 CFR §101.4; §101.9). Those required panels ordinarily don't tell you how a farm was run. Additional certifications and claims can address that, though they are not universal. Clothing has its own required label, plus optional claims and certifications. The opportunity is to make how a material was produced easier to compare across products, while recognizing the good disclosure already being done. Read the companion article about the cracker box and the clothing label.
PWW's Integrity Score examines brand evidence across its published methodology. Use it as one aid to inquiry, not a stand-in for the product-specific facts above. Asking for better information is a cooperative project: producers, growers, makers, researchers, and shoppers can all benefit from standards that make real work visible.