A 2016 study funded by Patagonia found that a single fleece jacket releases an average of 1.7 grams of microfibers per wash. Scaled across the billions of polyester garments washed globally every week, that number becomes almost impossible to picture.
Polyester is the most widely produced synthetic fiber in the world. For women choosing non toxic activewear collection options, it is also the fiber most worth understanding before making a decision. The evidence has been building for over a decade and it is not ambiguous. For the complete reference on microplastics in activewear including how they enter the body and what the health research says, the dedicated guide to microplastics in activewear covers it in full.
Why Polyester Sheds
Polyester is polyethylene terephthalate, abbreviated as PET, which is the same polymer used in plastic bottles and food packaging. When it is spun into fiber and woven or knitted into fabric, the polymer chains are intact but the surface area of the material increases enormously. Billions of tiny fiber ends are exposed across the face of any polyester garment.
Those fiber ends shed. Every time the fabric is flexed, rubbed, stretched, or agitated in water, individual fibers and fiber fragments break free. The finer the yarn and the tighter the knit, the more fiber ends are present, which is part of why performance activewear, designed with fine, close-knit structures for comfort and compression, tends to shed more than thicker, looser polyester constructions.
The Research Is Not New
Browne et al. (2011), writing in Environmental Science and Technology, documented synthetic microfibers in marine sediment samples from 18 shorelines across 6 continents and traced them to textile washing as a primary source. This study established the direct link between domestic laundry and environmental microfiber contamination.
That was 2011. The science since then has not softened the finding.
De Falco et al. (2019) published a study in Science of the Total Environment examining microfiber release from polyester fabrics specifically, finding that fabric construction, wash temperature, and spin speed all affect shedding volume, but none of those variables eliminate it. The conclusion was that shedding is inherent to polyester textiles, not a problem that can be engineered around without fundamentally changing the fiber.
A study by Napper and Thompson (2016) in Marine Pollution Bulletin tested polyester fleece, polyester-cotton blends, and acrylic fabrics under simulated washing conditions. Polyester-cotton blended fabrics released nearly 138,000 fibers per kg of fabric per wash. Acrylic released more, but polyester was a consistent and substantial shedder.
The Washing Machine Is Not the Only Source
Most of the public conversation about microfiber shedding focuses on washing. That is where the most concentrated release happens, and it is where filtration solutions like washing bags and machine filters can provide partial mitigation.
But polyester also sheds during wear. Abrasion between the fabric and skin, between fabric layers, and against equipment like gym mats, weights, or car seats generates fiber release throughout the day. A 2020 study in Environmental Science and Technology Letters documented airborne microfiber concentrations in indoor environments and identified clothing as a primary ongoing source, even outside of laundry events.
For activewear specifically, the wear-shedding question matters more than it does for other garment categories. Activewear is worn during intense physical movement, pressed closely against the skin, and often worn for extended periods before washing. The shedding that occurs during a workout happens directly against your body.
What Happens to Shed Fibers
Fibers that enter waterways during washing are documented in ocean sediments, freshwater systems, drinking water sources, and marine organisms. Thompson et al. (2004), in Science, was among the first to identify synthetic particles accumulating in marine environments. Subsequent research has tracked them through the food chain.
For fibers shed during wear, the exposure pathway is more direct. They enter the air in enclosed spaces, settle on surfaces, and are inhaled or ingested. Leslie et al. (2022), in Environment International, detected microplastics including synthetic polymer particles in human blood, establishing that absorption into the bloodstream is occurring. Researchers identified polyester fibers specifically in lung tissue samples from patients undergoing surgery (Jenner, L.C., et al., 2022, Science of the Total Environment), indicating inhalation as a real exposure route.
The health implications of inhaled and absorbed synthetic polymer particles are an active area of research. The data on their presence in human tissue is settled. What remains under investigation is the dose-response relationship and the specific biological effects at the concentrations people are accumulating.
Polyester in Activewear Is Particularly High-Exposure
Activewear presents a higher-exposure scenario than most clothing categories for two reasons. First, activewear is designed for movement and body contact, which maximizes both the mechanical shedding that happens during wear and the skin surface area exposed to shed particles. Second, activewear is worn during exercise, when the body's pores are open and skin absorption is potentially higher.
A 2021 analysis in the journal Sustainability examined microplastic absorption potential through skin and noted that during exercise, when sweating and elevated skin temperature occur, the conditions for transdermal absorption of particles and chemical leachates are more favorable than during rest.
This does not mean any specific harm outcome has been established. It means the exposure is not trivial, and the people most exposed are the people who wear synthetic activewear regularly.
A Different Approach
TENCEL Lyocell is a cellulosic fiber, not a synthetic polymer. It is derived from plant cellulose and processed without petroleum chemistry. When it breaks down through wear or washing, the fragments are biodegradable cellulosic material, not plastic particles. The shedding mechanism that makes polyester a microplastic source does not apply to TENCEL in the same way.
Kaplan et al. (2014), in Fibers and Polymers, documented TENCEL's moisture management and thermal comfort advantages in active wear applications. The functional case for TENCEL in activewear does not require setting aside performance. It requires weighing performance against the full picture of what a fabric does, including what it leaves behind. The nylon question is closely related, and whether nylon has microplastics covers that specifically. And for what else is chemically present beyond the fiber itself, toxic chemicals in workout clothes covers the finishing treatments that add a second layer of concern. For the full comparison of synthetic versus TENCEL, synthetic activewear versus TENCEL Lyocell goes deeper on performance.
Bellissima's Sempre Leggings are made from 92% TENCEL Lyocell. The 8% spandex content is there for stretch retention, and spandex does shed synthetic microfibers. That is disclosed because accuracy matters more than a clean marketing claim. What the 92% primary fiber does is shift the bulk of the fabric's shedding profile away from petroleum-derived plastic.
The Full Picture
Polyester performs. That is the honest answer, and the reason it became the default fiber for activewear globally. It is also a plastic that sheds microplastic particles into your body, your home, and your environment every time it is worn and washed. Those two things are both true.
What you do with that information is a choice. But it should be an informed one.
Sources
Browne, M.A., et al. (2011). Accumulation of microplastic on shorelines worldwide: sources and sinks. Environmental Science and Technology, 45(21).
De Falco, F., et al. (2019). Microfiber release to water, via laundering, and to air, via everyday use. Science of the Total Environment.
Napper, I.E., and Thompson, R.C. (2016). Release of synthetic microplastic plastic fibres from domestic washing machines. Marine Pollution Bulletin, 112(1-2).
Thompson, R.C., et al. (2004). Lost at sea: where is all the plastic? Science, 304(5672).
Leslie, H.A., et al. (2022). Discovery and quantification of plastic particle pollution in human blood. Environment International, 163.
Jenner, L.C., et al. (2022). Detection of microplastics in human lung tissue using muFTIR spectroscopy. Science of the Total Environment, 831.
Kaplan, S., et al. (2014). Thermal comfort of lyocell and other fibers in active wear. Fibers and Polymers, 15(6).
