For years, polyester was the default. It was everywhere in activewear, it performed well on the surface, and no one was asking hard questions about what it was doing beyond wicking sweat and holding shape through a squat.
We started asking those questions. The answers are why Bellissima exists. For anyone building a wardrobe of non toxic activewear, those questions are worth working through in full.
The Performance Story Was Always Incomplete
Polyester does what it claims to do. It wicks moisture along its surface. It holds stretch recovery through repeated wear. It is durable, colorfast, and relatively inexpensive to produce. Those are real properties and the reason the activewear industry standardized on it.
What the performance story left out was what polyester is made of, what it does beyond the listed properties, and what the cost of those properties actually is.
Polyester is polyethylene terephthalate. PET. The same polymer as a plastic bottle. When it is worn, it sheds plastic microfibers. When it is washed, it releases hundreds of thousands of those fibers into the water system per cycle, as documented by Napper and Thompson (2016) in Marine Pollution Bulletin. When it sits against skin during a sweaty workout, the warm, moist microclimate it creates does not absorb sweat so much as trap it, creating conditions that favor bacterial growth and, over time, permanent odor that no amount of washing fully reverses.
And that is before getting to what was applied to the fabric before it arrived. PFAS-based durable water repellent coatings were standard practice across the activewear industry, confirmed by the Texas Attorney General's 2026 investigation into Lululemon, which found PFAS had been used in their DWR products through early 2024. None of that is on the fiber content label. The full picture on toxic chemicals in workout clothes covers each category of chemical finishing in detail.
The Moment the Question Became Impossible to Ignore
The research on microplastics in human tissue is what changed the framing from environmental concern to personal health concern. Leslie et al. (2022), in Environment International, detected microplastic particles in human blood. Jenner et al. (2022), in Science of the Total Environment, found microplastic fibers in human lung tissue. Ragusa et al. (2021) found them in placental tissue. Marfella et al. (2024), in the New England Journal of Medicine, found microplastic particles in carotid artery plaque and associated their presence with significantly higher rates of cardiovascular events.
The particles are polyethylene terephthalate. PET. Polyester.
At that point the question stopped being abstract. The fiber that most activewear is made from is the same polymer type being found in human blood and tissue. The conditions of exercise, elevated skin temperature, open pores, active sweating, are the conditions that maximize absorption. The people most likely to be accumulating polyester-derived microplastics through clothing contact are people who exercise regularly in polyester activewear. That is a significant portion of the health-conscious consumer market. The research on how microplastics interact with hormones is one of the most consequential areas of that picture.
What We Built Instead
TENCEL Lyocell is not a synthetic polymer. It is derived from sustainably harvested wood pulp, processed in a closed-loop system using a non-toxic solvent with a recovery rate above 99%, according to Lenzing AG's published production documentation. It does not shed petroleum-derived plastic microfibers. It carries OEKO-TEX Standard 100 and EU Ecolabel certification, meaning it has been independently tested for harmful substances including phthalates, PFAS, formaldehyde, and heavy metals.
Its moisture management is structural. Kaplan et al. (2014), in Fibers and Polymers, documented TENCEL's superior moisture regulation and thermal comfort in active wear settings compared to synthetic alternatives. It absorbs sweat into the fiber's core rather than allowing it to accumulate at the surface, which changes the bacterial environment, changes the odor profile over repeated wears, and changes the exposure conditions at the skin-fabric interface during exercise.
The Sempre Leggings are built on that fiber. 92% TENCEL Lyocell, 8% spandex for stretch retention. The spandex is disclosed because the full composition is what matters. The primary fiber is not a plastic polymer, and that is not a minor distinction.
The Switch Is Not a Compromise
The concern we heard when we started talking about this publicly was that moving away from polyester meant accepting worse performance. That the non-toxic choice was the less functional one.
It is not. TENCEL performs. The moisture management is different in mechanism but effective in outcome. The feel against skin is noticeably different, softer and more stable through a workout, without the synthetic surface friction that makes polyester feel increasingly uncomfortable as it gets wet. The odor profile over repeated wears is categorically different because the bacterial conditions that create permanent odor in polyester do not develop in the same way in a hydrophilic fiber.
The switch is not a compromise. It is a better product built on a better material, for people who exercise regularly and want to know what they are wearing while they do it. For a broader look at what this means at the cost level, the hidden cost of cheap activewear works through the full financial and health accounting. And for the current regulatory picture, whether Lululemon is non-toxic in 2026 illustrates how far the industry has been from transparent on these questions.
We stopped wearing polyester workout clothes because we looked at what polyester workout clothes actually are. We think most people, given the same information, would make the same call.
Sources
Napper, I.E., and Thompson, R.C. (2016). Release of synthetic microplastic plastic fibres from domestic washing machines. Marine Pollution Bulletin, 112(1-2).
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.
Ragusa, A., et al. (2021). Plasticenta: First evidence of microplastics in human placenta. Environment International, 146.
Marfella, R., et al. (2024). Microplastics and nanoplastics in atheromas and cardiovascular events. New England Journal of Medicine, 390(10).
Texas Attorney General. (2026, April 13). Attorney General Ken Paxton Launches Investigation into Lululemon Over Potential Presence of Toxic "Forever Chemicals" in Activewear. texasattorneygeneral.gov.
Lenzing AG. (2023). TENCEL Lyocell: Production Process. Lenzing.com.
Kaplan, S., et al. (2014). Thermal comfort of lyocell and other fibers in active wear. Fibers and Polymers, 15(6).
