Most athletic wear is built from synthetic fibers, primarily polyester, nylon, and a stretchy fiber called elastane (often sold under the brand name Lycra or spandex). A typical pair of leggings or workout top contains 80 to 90 percent polyester or nylon, with 10 to 20 percent elastane blended in for stretch. These ratios shift depending on the activity the garment is designed for, and newer options made from natural or semi-synthetic fibers are gaining ground. Here’s what goes into each type and why it matters.
The Three Core Synthetic Fibers
Polyester is the workhorse of athletic clothing. It’s lightweight, holds its shape through repeated washing, and dries quickly because it barely absorbs water. Instead of soaking up sweat, polyester moves it along the surface of the fabric to evaporate. That’s why you’ll find it in running shirts, gym shorts, and most high-intensity workout gear.
Nylon is softer against the skin and has a silkier feel, which makes it popular in yoga pants, sports bras, and everyday athleisure pieces. It’s slightly more absorbent than polyester, so it can feel a bit cooler in moderate heat, but it also takes longer to dry.
Elastane is what gives athletic clothing its stretch. On its own, neither polyester nor nylon stretches much. Even a small percentage of elastane, around 10 to 15 percent, allows a garment to move with your body and snap back to its original shape. Higher-compression garments like swimwear and medical-grade compression leggings push that ratio much higher, sometimes reaching 20 to 25 percent elastane or even more for clinical-grade support.
How Blends Change by Activity
Fabric engineers adjust the ratio of these fibers depending on what the garment needs to do. The differences are meaningful if you’re choosing workout clothes for a specific purpose.
- Running, HIIT, and cycling: 80 to 90 percent polyester with 15 to 20 percent elastane. Polyester’s fast-drying properties handle heavy sweat, while the higher elastane content adds compression and support during explosive movements.
- Yoga and Pilates: 80 to 90 percent nylon with 10 to 20 percent elastane. Nylon’s softer hand feel and four-way stretch make it more comfortable for floor work and deep stretches.
- Swimming: 80 to 85 percent nylon or polyester with 15 to 20 percent elastane. The higher elastane content keeps the suit snug and in place against water resistance. Chlorine breaks down elastane over time, so polyester-blend swimsuits tend to last longer in pool settings.
- Hiking and outdoor sports: 85 to 90 percent polyester with 10 to 15 percent elastane, often with a brushed or fleece-lined interior for warmth.
- Athleisure and casual wear: 80 to 85 percent nylon with 15 to 20 percent elastane, prioritizing soft feel and everyday comfort over peak sweat performance.
How Moisture-Wicking Actually Works
The phrase “moisture-wicking” appears on nearly every athletic garment, but the mechanism is surprisingly simple. It relies on capillary action: the same force that pulls water up through a thin straw or a paper towel. Water molecules are naturally attracted to surfaces, and when the spaces between fibers are small enough, that attraction pulls sweat outward through the fabric faster than gravity can pull it down.
Standard yarn has a round cross-section, which means individual fibers pack tightly together and leave little room for water to travel. Performance fabrics solve this by using fibers with unusual cross-sections: triangular, cross-shaped, or channeled. When these oddly shaped fibers are woven together, tiny gaps form between them. Those micropores create the perfect pathways for capillary action, pulling sweat from your skin to the fabric’s outer surface where it evaporates into the air. This is why two polyester shirts can feel completely different during a workout. The fiber shape and weave structure matter as much as the fiber type.
Natural and Semi-Synthetic Alternatives
Synthetics dominate activewear, but natural and plant-based fibers are increasingly competitive for certain activities.
Merino wool is the standout. It regulates body temperature in both directions: warming you when it’s cold and cooling you when it’s hot. In direct testing, wool showed 96 percent better moisture buffering than polyester, 45 percent better than cotton, and 26 percent better than viscose. It also resists odor naturally because bacteria don’t thrive on its fibers the way they do on polyester. That makes merino a strong choice for multi-day hiking trips or any situation where you can’t wash your clothes frequently. The tradeoff is cost and durability; merino is significantly more expensive and tends to develop holes faster than synthetics.
Tencel, a fiber made from wood pulp, is gaining traction in activewear blends. It absorbs significantly more moisture than polyester and does so faster. At 90 percent relative humidity, Tencel absorbs about as much water vapor as wool or down. It also produces a measurable cooling effect. Skin temperature under Tencel fabric runs about 0.5 to 1 degree Celsius lower than under synthetic fabric during heavy sweating. That sounds small, but it’s physiologically significant. Even minority blends of 25 to 40 percent Tencel mixed with other fibers produce a noticeably cooler feeling than pure cotton or polyester. Tencel’s smooth fiber surface also makes it gentle on sensitive skin and resistant to static charge.
Water Repellency and the PFAS Shift
Outdoor athletic wear, particularly rain jackets and wind shells, has historically relied on a class of chemicals called PFAS (per- and polyfluoroalkyl substances) for water repellency. These “forever chemicals” are extraordinarily effective at making water bead up and roll off fabric. They’re also persistent in the environment and increasingly linked to health concerns.
The industry has moved decisively away from them. Gore-Tex released a PFAS-free membrane in 2022. In 2025, both New York and California banned the sale of apparel with intentionally added PFAS. Major brands like Arc’teryx, Patagonia, and Mountain Hardwear have switched to alternative water-repellent coatings, and early testing suggests some of these PFAS-free options perform comparably well.
If you want to verify that your gear is PFAS-free, look for the Bluesign label or Oeko-Tex certification. As of January 2025, neither certification permits PFAS in approved products. Worth noting: older rain jackets lose their water repellency over time as the original coating wears off, regardless of the chemistry involved, so periodic retreatment with a product like Nikwax is normal.
Recycled Polyester: Same Look, Slight Tradeoffs
Many athletic brands now use recycled polyester, often labeled rPET, made from post-consumer plastic bottles or reclaimed textile waste. It looks and feels nearly identical to virgin polyester in a finished garment. However, multiple studies have found that recycled polyester fibers have lower crystallinity and tensile strength than virgin fibers. In practice, this means recycled-polyester garments may pill or lose their shape slightly sooner over many wash cycles. For most casual and moderate-intensity use, the difference is hard to notice. For high-wear items like compression tights or daily-use leggings, it’s worth considering.
Microplastic Shedding During Washing
Every synthetic garment releases tiny plastic fibers when you wash it. A single laundry load can shed several million fiber fragments into the water. Not all fabrics shed equally. Loosely woven synthetics like fleece release far more microplastics than tightly woven fabrics, which hold together better during the wash cycle. If you want to reduce shedding, washing on a gentle cycle with cold water helps, and mesh laundry bags designed to capture microfibers (like the Guppyfriend bag) can trap a significant portion before they reach the drain.
Tightly knit performance fabrics, the kind used in compression leggings and fitted tops, shed less than their looser counterparts. This is one of those rare cases where the higher-quality construction you’d want for performance reasons also happens to be the better environmental choice.