Why natural fibers
The Plain Thread lists brands that sell natural fiber clothing: cotton, linen, wool, hemp, silk, alpaca, cashmere. We built it because of what synthetic clothing does in the wash and while you wear it.
Polyester, nylon, and acrylic garments shed plastic particles — microplastics — with every wash cycle and with every wear. Those particles are too small for water treatment to fully capture. They accumulate in rivers, oceans, drinking water, wildlife, and human tissue. The research below is peer-reviewed. All primary sources are linked.
What synthetic clothing sheds during washing
When a synthetic garment is washed, friction between fibers and water breaks off tiny plastic fragments. A single wash cycle releases between 100,000 and 6.3 million microplastic fibers per kilogram of synthetic textile — a range that varies more than 850-fold depending on fabric type. Polyester softshell sheds the most.
Tumble drying adds to this. Polyester fleece releases up to 1,700 mg of microplastic fibers per kilogram in a single drying cycle.
The fibers are 360 to 660 micrometers long and 12 to 16 micrometers in diameter — small enough to pass through most wastewater treatment processes.
Sources: Environmental Science and Pollution Research, Springer, 2021 (PMC7969573) · De Falco et al., Scientific Reports, Nature, 2019
The scale of the problem
Synthetic microfibers released into the environment annually from U.S. and Canadian laundry, after wastewater treatment.
PLOS ONE, 2021Microplastic fibers a single wastewater treatment facility can release into receiving water bodies per day, even at 98%+ removal efficiency.
Murphy et al., ACS Environmental Science and Technology, 2016Share of global primary microplastic ocean pollution attributable to synthetic textiles — the single largest primary source category. (This figure applies to primary microplastics specifically, not all ocean plastic.)
Boucher and Friot, IUCN, 2017Where microplastics end up
The World Health Organization has identified microplastics in both tap and bottled drinking water globally. Current evidence is insufficient for a definitive health risk assessment — but microplastics are present throughout the drinking water supply.
WHO, Microplastics in Drinking-Water, 2019Chronic exposure to synthetic microplastic fibers causes aneurysms, surface erosion, and serious gill damage in fish. Laboratory testing found polyester microfibers toxic to sea urchin embryonic development at concentrations found in current marine environments.
PMC11510891, peer-reviewed, 2024; ScienceDaily reporting on peer-reviewed research, 2020A 2024 scoping review found microplastics detected in 8 of 12 human organ systems, including cardiovascular, respiratory, reproductive, and urinary systems.
Journal of Global Health, scoping review, 2024 (PMC11342020)A 2023 study found nine types of microplastics across five types of cardiac tissue in patients undergoing open-heart surgery, including in pre- and postoperative blood samples. The largest particle measured 184 micrometers.
ACS Environmental Science and Technology, 2023 (PMID 37440474)A 2025 Nature Medicine study detected microplastics in human brain tissue at concentrations substantially higher than liver or kidney tissue (brain ~4,917 µg/g; liver ~433 µg/g; kidney ~404 µg/g; p < 0.0001).
Nihart et al., Nature Medicine, February 2025What the research does not yet show
The presence of microplastics in human tissue has been confirmed across multiple independent studies. What has not been established is a causal relationship between microplastic exposure and specific health outcomes. The findings above are detection-based — they show microplastics are present, not what level causes harm. Research into dose-response relationships and health effects is ongoing.
What natural fibers do differently
Natural fibers — cotton, linen, wool, hemp, silk, alpaca, cashmere — do not contain synthetic polymers. They do not shed microplastics during washing or wear. When they shed fibers, those fibers are organic and biodegradable.
Every brand in this directory sells clothing made from these fibers.
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