Natural fiber vs synthetic fiber
The fundamental difference is origin. Natural fibers come from plants and animals — cotton, wool, linen, hemp. Synthetic fibers are manufactured from petroleum — polyester, nylon, acrylic. That difference determines everything else: whether the fiber biodegrades, whether it sheds microplastics, and what happens to it at end of life.
| Natural fibers | Synthetic fibers | |
|---|---|---|
| Source | Plants and animals | Petroleum (crude oil) |
| Examples | Cotton, wool, linen, hemp, silk, alpaca | Polyester, nylon, acrylic, spandex |
| Microplastic shedding | None | 100,000 to 6.3 million fibers per wash cycle per kg of fabric |
| Biodegradable | Yes | No — persists for hundreds of years |
| Breathability | High — natural fiber structures allow airflow | Lower — synthetic fibers trap heat |
| Odor resistance | Natural (especially wool and merino) | Requires chemical treatments (PFAS, antimicrobials) |
| Chemical treatments | Minimal when certified (GOTS, OEKO-TEX) | Often required for performance features |
| End of life | Biodegrades | Persists in landfill and environment |
The microplastics difference
This is the most significant practical difference for anyone buying clothing today. Synthetic fibers shed microplastic particles during every wash. Research published in Environmental Science and Pollution Research (2021) measured between 100,000 and 6.3 million microplastic fibers released per kilogram of synthetic textile per wash cycle. These particles are 360 to 660 micrometers long — small enough to pass through wastewater treatment.
Natural fibers do not contain synthetic polymers. They do not shed microplastics. When natural fiber fragments enter waterways, they biodegrade.
Researchers have now detected microplastics in 8 of 12 human organ systems, including cardiac tissue in surgical patients and brain tissue at concentrations higher than any other organ measured. Research into health effects is ongoing; causal mechanisms have not yet been established.
Performance
Synthetic fibers became dominant in apparel because they are cheap to produce and can be engineered for specific performance characteristics. The common argument is that synthetics outperform natural fibers in activewear.
Merino wool performs comparably to synthetic base layers in temperature regulation, moisture management, and odor resistance — without chemical treatments and without shedding microplastics. Many performance characteristics attributed to synthetics require chemical additions (PFAS for water resistance, antimicrobial treatments for odor control) that natural fibers provide inherently.
Every brand in The Plain Thread directory uses natural fibers as their primary material. No synthetics.
Browse clothing brands