Merino Short - 5"
Designed for everyday movement in merino.
Shop nowAntimony & The "Sweat Effect": The Heavy Metal Risk in Recycled Polyester
In the quest for sustainable fashion, recycled polyester (rPET)—often made from diverted plastic water bottles—has been hailed as a miracle fabric. It promises to keep plastic out of landfills while providing the "performance" stretch we’ve come to expect from our leggings and sports bras. However, while the headlines focus on BPA and PFAS, a more insidious risk remains largely ignored: Antimony.
Antimony trioxide is a heavy metal catalyst used in approximately 85% of all PET plastic production. It is the chemical "glue" that helps turn petroleum-based liquids into solid plastic fibers. When you wear recycled synthetics, you aren’t just wearing old water bottles; you are wearing a material embedded with heavy metals that are reactivated by the very thing activewear is designed for: your workout.
The "Sweat Effect": How Your Workout Unlocks Heavy Metals
The primary concern with antimony in polyester activewear isn't just its presence, but its mobility. In a stable, cold environment, antimony remains relatively locked within the plastic matrix. However, your body during a workout provides the three exact catalysts required for chemical leaching:
- Heat: As your core temperature rises, the molecular structure of synthetic fibers relaxes, allowing embedded chemicals to migrate to the surface.
- Moisture (The Solvent): Sweat is not just water; it is a complex fluid with varying pH levels. Research indicates that sweat acts as a solvent, pulling heavy metals in clothing out of the fabric and onto the skin.
- Friction: The repetitive motion of running, cycling, or yoga creates mechanical stress on the fibers, further accelerating the release of toxic particulates.
This "Sweat Effect" creates a delivery system where antimony leaching sweat meets your skin at the exact moment your pores are most dilated and permeable. If you have ever wondered, is polyester activewear bad for skin?, the answer lies in this chemical migration.
Is Recycled Polyester Toxic? The rPET Paradox
There is a common misconception that "recycled" means "purified." In reality, the recycling process for rPET is often mechanical, meaning the original plastic is shredded and melted down. This process does not remove the antimony used in the initial production. In some cases, the repeated heating cycles of recycling can make the fibers more prone to degradation, potentially increasing the rPET health risks compared to virgin polyester.
Furthermore, because your skin is a semi-permeable organ rather than a solid barrier, the heavy metals and endocrine disruptors found in these garments can migrate directly into your bloodstream. This raises a critical question for the health-conscious mover: Are my gym clothes messing with my hormones? When we consider the cumulative exposure to antimony—a suspected carcinogen and known skin irritant—the "eco-friendly" narrative of recycled plastic begins to unravel.
Merino Wool: The Catalyst-Free Alternative
At Estroni, we believe that activewear should support your physiology, not challenge it. Unlike synthetic "performance" fabrics that rely on heavy metal catalysts and chemical finishes to manage moisture, Merino wool is a bio-compatible fiber. It is grown, not manufactured in a lab, meaning it is naturally free from antimony and other petroleum-based catalysts.
Merino wool works with your body’s cooling system proactively. While polyester is hydrophobic (it hates water) and waits for you to turn into a puddle before "wicking" sweat away, Merino absorbs moisture at the vapor stage. By removing the humidity from the air next to your skin before it turns into liquid, Merino prevents the very conditions that lead to chemical leaching.
Why We Use a 95/5 Blend
While 100% natural fibers are the goal for purity, high-intensity movement requires structural integrity. Pure Merino, while beautiful, can lose its shape or develop holes under the stress of a heavy gym session. To solve this, we utilize a 95% Merino and 5% Elastane blend.
This tiny percentage of elastane provides the "snap-back" and durability needed for leggings and bras, while ensuring that the primary fiber against your skin is pure, breathable, and catalyst-free wool. For a deeper look at why we chose this specific composition, read our guide on 100% Merino vs 95/5 Blends: Which Is Better for Activewear?.
Choosing Low-Tox Movement
The activewear industry has spent decades marketing "recycled plastic" as a solution to environmental woes. But as we learn more about the science of the skin microbiome and heavy metal leaching, it’s clear that wearing plastic bottles is a compromise our bodies shouldn't have to make.
By choosing natural fibers, you aren't just opting out of the microplastic cycle; you are protecting yourself from the invisible "Sweat Effect" of heavy metals. It’s time to move away from treated plastics and return to materials that were designed by nature to move, breathe, and protect.
