What the popular framing says
The conversation around microplastics in clothing has settled into a familiar structure. Polyester sheds microplastics. Cotton does not. Choose natural fibers and you are not part of the problem.
This framing appears across social media and product pages for natural fiber activewear brands. The logic is intuitive: plastic fabrics shed plastic fibers; natural fabrics do not shed anything problematic.
The framing is half right. The half it gets wrong matters for how you spec a product and how you defend a claim.
What does the shedding data actually say?
A 2021 study published in PLOS ONE evaluated microfiber release from 37 consumer apparel textile samples across five consecutive domestic laundry cycles. The findings disrupt the popular framing.
Textiles made with nylon shed less (mean of 27 ± 14 mg/kg of textile per wash) than those made with polyester (mean of 161 ± 173 mg/kg of textile per wash).
Here is the number that challenges the assumption: cotton and wool textiles also shed large amounts of microfibers (165 ± 44 mg/kg per wash).
Read that again. Cotton and wool shed at rates statistically indistinguishable from polyester. The mean for cotton and wool was 165 mg/kg. The mean for polyester was 161 mg/kg. The difference is within the margin of error.
Microfiber loss ranged from 9.6 mg to 1,240 mg/kg of textile per wash, or an estimated 8,809 to more than 6,877,000 microfibers. The variation depends on construction, mechanical treatment, yarn type, and fabric weight.
Mechanically-treated polyester samples, dominated by fleeces and jerseys, released six times more microfibers (161 ± 173 mg/kg per wash) than did nylon samples with woven construction and filamentous yarns (27 ± 14 mg/kg per wash).
Construction matters more than fiber type for raw shedding numbers. A brushed fleece sheds more than a woven nylon shell. A loose-knit cotton jersey sheds more than a tight-weave polyester.
Does construction affect shedding rate?
Yes. The data is unambiguous on this point.
All textiles were found to shed, but polyester fleece fabrics shed the greatest amounts, averaging 7,360 fibers per square meter per liter in one wash, compared with polyester fabrics which shed 87 fibers per square meter per liter.
That is an 84-fold difference between fleece and standard polyester, same polymer, different construction.
We found that loose textile constructions shed more, as did worn fabrics, and high twist yarns are to be preferred for shed reduction.
Polyester garments (blankets, fleeces, and shirts) can shed more than 1,900 fibers per wash. All garments released more than 100 fibers per liter of effluent, with more than 180% more from fleeces than other construction types.
This applies to natural fibers too. A loose-knit slub cotton with short staple fibers will shed more than a tight-weave long-staple cotton. Tighter construction, longer staple lengths, and filament yarns (where available) will outperform fuzzy, brushed, or loosely knit fabrics regardless of fiber type.
Where the popular framing is right
The popular framing is right about persistence.
Using well-controlled aquatic biodegradation experiments it was shown that cotton and rayon microfibers are expected to degrade in natural aquatic aerobic environments whereas polyester microfibers are expected to persist in the environment for long periods of time.
The findings show that over the course of 102 days, cotton microfibers treated with textile finishes (silicone softener, durable press finish, water repellent finish, and a blue dye) biodegrade by more than 60%; a rate greater than or comparable to that of an oak leaf.
That 2021 study from NC State University, Duke University, and Cotton Incorporated tested cotton with actual industrial finishes. Not raw fiber. Finished fabric. The finishes did not prevent biodegradation.
Polyester microfibers show very little degradation in all three aquatic environments and are expected to persist in the environment for long periods of time based on the data trend chart. Cellulosic fibers (those from cotton and rayon) degrade significantly more than petroleum-based microfibers.
The mechanism is straightforward. Cotton is cellulose. Wool is keratin. Both are organic polymers that microorganisms can metabolize. Polyester is polyethylene terephthalate. It is not metabolizable by any known organism at environmentally relevant timescales.
"Natural plant fibers like cotton readily biodegrade and petroleum-based microfibers do not, leaving fewer microfibers (and no microplastics) behind."
What about wool biodegradation?
Wool is a natural keratin protein fiber used in apparel, floor coverings, and technical applications. Synthetic fibers from textiles are one source of microplastic pollution as fibers may be released from garments during use and especially during laundering, whereby they may enter the aquatic environment via wastewater systems.
One early study showed that wool biodegraded in the natural marine environment, demonstrating there are microorganisms in the ocean that biodegrade wool keratin.
Scientists found untreated wool biodegraded at 20.3 per cent the rate of the pulp and the machine-washable wool biodegraded more than three times as quickly, at a rate of 67.3 per cent, the fastest of all fabrics.
Machine-washable wool, treated with chlorine and Hercosett resin for shrink resistance, actually biodegrades faster than untreated wool in marine environments. The polyamide-epichlorohydrin treatment caused the wool to biodegrade more rapidly because it removes some of the fiber's cuticle, making it more susceptible to microorganisms in the ocean that target keratin.
Research shows that wool biodegrades readily in a marine environment and does not contribute to long-term microfiber pollution. This holds for both untreated wool and machine-washable wool.
Where the popular framing is wrong, and the mechanism for why
The popular framing is wrong about shedding itself. It tells consumers that natural fibers do not shed. The data says natural fibers shed at comparable rates.
This matters for three reasons.
1. Regulatory scope is expanding beyond plastics
Microfiber: Any synthetic or natural textile fiber that is less than 5 millimeters in length.
That is the definition in the Fighting Fibers Act of 2025, currently before Congress. The Fighting Fibers Act of 2025 introduced by Senator Jeff Merkley and Rep. Mike Levin focuses on one of the most significant sources of this pollution: our laundry. The Act would require all new washing machines to include microfiber filtration and would also commission research on the impact of microfibers in our water.
Starting January 1, 2030, all new washing machines sold or offered for sale in the United States must include a microfiber filtration system.
The bill does not exempt natural fibers. Filters will capture cotton and wool fibers too. Global Policy Momentum: Australia, New South Wales, the United States (via Oregon SB 526 and the federal Fighting Fibers Act of 2025), and the UK are actively proposing or implementing filter requirements.
France's 2025 Mandate: All new washing machines sold in France must include a microfiber-capture solution from January 1, 2025, under the AGEC law.
2. Shedding claims need precision
If your product page says "does not shed microplastics," that claim is defensible for 100% cotton or wool. If your product page says "does not shed microfibers," that claim is not defensible. The lab data contradicts it.
The distinction is subtle but real. Microplastics are synthetic. Microfibers include both synthetic and natural. Your copy needs to use the right term.
3. Construction still matters
Thicker and fluffier synthetic fabrics, especially those made from polyester, are notorious for shedding microfibers. Knit fabrics and fleece are generally more prone to shedding microfibers than woven fabrics.
This applies to natural fibers too. Cotton released the highest number of microfibers, averaging 617.34 ± 85.2 mg/kg per wash, while nylon released the least, with 225.12 ± 30 mg/kg per wash. Different studies show different absolute values depending on the specific fabrics tested, but the pattern holds: construction drives shedding as much as fiber type.
How do the standard test methods work?
AATCC TM212-2021 provides a standardized method for quantifying fiber fragment shedding in the ongoing challenge to combat aquatic pollution.
AATCC TM212 measures fiber fragment release during simulated home laundering. Using an accelerated washing machine, it quantifies the mass of shed microfibers, making it an ideal test for assessing washable textiles.
The test uses gravimetric analysis: weigh the fabric before, wash under controlled conditions, filter the effluent, dry and weigh the captured fibers. The result is milligrams of fiber per kilogram of textile per wash cycle.
ISO 4484 offers a broader approach compared to the previous standard. ISO 4484-1 focuses on material loss from fabrics during washing, while ISO 4484-3 evaluates shedding from finished products like garments.
Originally assumed to be a plastics problem, natural fibers are also appearing in marine life's food cycle. AATCC TM212 is not limited to man-made fibers, as it can be used to determine the fiber shedding potential of natural fibers and blends.
This is the methodological point the popular framing misses. The tests quantify mass loss. They do not distinguish between fibers that biodegrade and fibers that persist.
What does social commentary say about this?
The social media discourse has picked up half the story. There aren't many studies that draw conclusions about how all this microplastic is affecting our health and the health of our planet. "For lots of that research, we're kind of at the point of understanding just where the plastics are, and then once we understand where they are, trying to figure out what impact they're having."
Creators are correctly identifying that polyester sheds microplastics that persist in the body and environment. What the discourse underemphasizes: natural fibers shed too, but those fibers biodegrade. The relevant comparison is not shedding rate. It is what happens after shedding.
What this means for a product founder
If you are building a natural fiber activewear line, here is what the data actually supports:
Defensible claim: "Our fabrics do not shed microplastics." This is true for 100% natural fiber constructions. Cotton, wool, linen, and hemp fibers are not plastic.
Not defensible: "Our fabrics do not shed microfibers." All textiles shed. The lab data is unambiguous.
Strongest positioning: "Our fabrics shed microfibers that biodegrade within months, not centuries." This is the evidence-backed distinction. It requires you to explain the difference, which is harder than a simple claim but more accurate.
Construction spec implications:
- Tighter weaves shed less than loose knits
- Filament yarns shed less than staple yarns
- Less mechanical finishing (brushing, napping) means less shedding
- Longer staple cotton sheds less than short staple
- High twist yarns shed less than low twist
OHZEN-TEX(TM) protocols include both shedding rate testing and fiber composition verification, because the two metrics together tell the story that either alone does not.
Regulatory preparation: If the Fighting Fibers Act passes, washing machine filters will capture natural fibers too. Your marketing cannot ignore that natural fibers shed. It can emphasize that they biodegrade.
The relevant number is not shedding rate. It is biodegradation rate. That is the metric where natural fibers win.
Sources
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