Every time a synthetic garment is washed, it sheds fibres. A single wash cycle can release hundreds of thousands of microplastic particles — fragments and filaments under five millimetres in length — into the wastewater. Most pass through sewage treatment plants, which are designed to filter pathogens and dissolved chemicals rather than plastic particles. They enter rivers, estuaries, and eventually oceans.
The scale of the problem is significant. Synthetic textiles are estimated to account for 35 percent of primary microplastics in the ocean. Studies have found microplastics in marine wildlife, in table salt, in drinking water, in human blood and lung tissue. The health implications are not yet fully understood, but the trajectory of the science is concerning.
Which fabrics shed most
Not all synthetics shed equally. The key variables are fibre type, fabric construction, and garment age.
Acrylic sheds the most heavily of the common synthetic textiles — some studies suggest it releases more than five times the fibres of polyester per wash. Polyester fleece, popular in outdoor and casual clothing, releases large quantities of fibres because of its brushed surface area. Woven polyester sheds considerably less than knit polyester because the interlocking structure holds fibres more securely.
Older garments shed more than new ones, because fibres that would eventually release have already done so in earlier washes. There is a case — counterintuitive — for keeping synthetic garments and washing them until they have reached a lower shedding equilibrium, rather than replacing them with new items that will shed heavily in their early wash cycles.
Natural fibres biodegrade, so the question of persistence in the environment does not apply in the same way. They still shed — natural fibre fragments are found in the ocean — but they break down rather than accumulating indefinitely.
What reduces shedding
Washing bags designed to capture fibres — the Guppyfriend bag is the most widely tested — physically trap released particles, preventing them from entering the wastewater. Studies suggest they reduce fibre release by 80-90 percent when used correctly and the collected fibres are disposed of in solid waste rather than rinsed away. They are a practical, inexpensive intervention.
Washing machine filters designed to capture microplastics at the appliance level offer a more passive solution. Several manufacturers have introduced retrofittable units. Legislation in France requires new washing machines to include microplastic filters from 2025; similar requirements are being considered in other jurisdictions.
Lower spin speeds reduce the mechanical agitation that tears fibres loose. Shorter cycles achieve the same result. Cold water may also reduce shedding slightly compared to warm. A full drum sheds less per kilogram of laundry than a partial load, because garments have less room to tumble and abrade against each other.
The bigger picture
Individual behaviour matters, but the scale of synthetic textile production — one of the considerations in the eco criteria for brands — means upstream intervention is more consequential makes upstream intervention more consequential. Reducing the volume of new synthetic garments produced addresses the source. Better fabric construction — tighter weaves, higher-quality yarn, more durable fibres — reduces shedding per garment. Industry standards for shedding rates are being developed in several countries.
The practical position for a consumer: a Guppyfriend bag and lower spin speeds are straightforward steps with evidence behind them. Washing less frequently, when hygiene permits, reduces total wash cycles and total fibre release. Choosing natural fibres where performance requirements allow avoids synthetic shedding entirely. None of these fully solve a structural problem, but they reduce a household’s contribution to it.