Materials 101

Synthetic Fibers

Petroleum-derived, non-biodegradable, and woven into most of what hangs on store racks today. Here is what each one is, how it is made, and what it costs.

Petroleum-Based Synthetic

Structural Synthetics

The foundation of the modern clothing market is petroleum-based synthetic fibers. They dominate global fashion because they’re cheap to produce, not because they’re better for you. Worn against your skin for hours every day, these fabrics trap heat, hold odor, and shed microscopic plastic particles. Those same microplastics have now been found in human blood, lung tissue, and even the placenta.

Key concerns

  • All shed microplastic particles with every wash
  • Poor breathability relative to natural fibers — traps heat and moisture against skin

Polyester

Polyethylene terephthalate (PET) — the same polymer used to make plastic water bottles — spun into fiber and woven into fabric. First developed in the 1940s, polyester now accounts for roughly 60% of global fiber output, making it the single most produced textile material on earth. It is durable, wrinkle-resistant, and cheap to manufacture, which has made it the industry default across nearly every clothing category.

Key concerns

  • Sheds microplastic fibers that can carry and hold hormone-disrupting chemicals against your skin during wear
  • Poor breathability relative to natural fibers — traps heat and moisture against skin
  • Many polyester fabrics use chemical finishes like moisture-wicking and antimicrobial treatments that may involve hormone-disrupting chemicals such as BPA

Nylon

Also called Polyamide

The world’s first fully synthetic fiber, developed by DuPont in 1935 as a replacement for silk in women’s hosiery. Made from polyamide polymers derived from petroleum, nylon is prized for its tensile strength, light weight, and abrasion resistance. Today it is used heavily in activewear, swimwear, hosiery, and outerwear.

Key concerns

  • Many nylon garments may use PFAS-based chemical finishes, aka 'forever chemicals,' associated with thyroid and reproductive effects
  • May contain processing additives like antistatic and finishing agents, some of which may contain hormone-disrupting chemicals that can transfer during wear
  • May use coatings containing bisphenol-related compounds like BADGE, raising concerns about hormone-disrupting chemical exposure through prolonged skin contact

Acrylic

Made from polyacrylonitrile, acrylic dominates as a cheap substitute for wool in mass-market knitwear, sweaters, and fleece. Soft in hand but fundamentally different in behavior. Acrylic pills aggressively, fails to regulate body temperature, and researchers consistently identify it as one of the most environmentally damaging fibers in global circulation.

Key concerns

  • Sheds more microplastic particles per wash than polyester or nylon
  • Often uses dyes and finishing chemicals that may irritate sensitive skin and can include compounds with endocrine-disrupting potential
  • Heavy pilling accelerates fiber shedding and shortens garment lifespan

Polypropylene

Produced from propylene, a byproduct of petroleum and natural gas refining, polypropylene is used primarily in performance base layers, athletic socks, and moisture-wicking underlayers. Because it is fully hydrophobic, it absorbs no water, which is marketed as a moisture-management advantage. In practice, sweat is displaced from the fiber surface but odor compounds accumulate rapidly, and the fiber cannot tolerate the high wash temperatures needed to fully clean it.

Key concerns

  • May use stabilizers and finishing additives with endocrine-disrupting potential
  • Some activewear uses antimicrobial odor-control treatments with chemical exposure concerns

Petroleum-Based Synthetic

Stretch Synthetics

One fiber, three names. Blended into nearly every category of modern clothing in small quantities, where it quietly disqualifies them from natural fiber standards.

Elastane

Also known as Spandex and Lycra — all the same polyurethane fiber

A polyurethane-based synthetic derived from petroleum, elastane can stretch up to 600% of its length and return fully to shape, resulting in the industry blending it into nearly everything. At just 2–5% by weight, it found its way into denim, underwear, socks, dress shirts, knitwear, and activewear, often with little consideration for the consequences.

Key concerns

  • Designed for tight, prolonged skin contact — especially in underwear and activewear, which can increase heat retention and reduce breathability
  • Tight synthetic underwear can increase scrotal temperature; clinical research has linked prolonged heat exposure to changes in sperm quality and reproductive markers
  • Some stretch garments use antimicrobial, stain-resistant, or water-resistant chemical treatments with endocrine-disrupting concerns
  • Contributes polyurethane-based microplastic shedding during washing and wear

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