Most athletic shirts are made from polyester, either on its own or blended with a small percentage of spandex for stretch. Nylon and merino wool are also common, each offering different trade-offs in breathability, durability, and odor control. The specific blend and fabric weight determine how a shirt performs during exercise, so understanding what goes into these materials helps you pick the right one.
Polyester: The Most Common Base Fabric
Polyester, sometimes listed as PET fiber on labels, dominates the athletic shirt market. It’s lightweight, durable, and holds its shape well after repeated washing. On its own, polyester doesn’t absorb much moisture. The “moisture-wicking” versions you see on tags rely on special fiber treatments or engineered cross-section shapes that pull sweat away from your skin through tiny channels in the fabric. This works through capillary action: the narrow spaces between fibers create a pumping effect that draws liquid outward, where it spreads across a larger surface area and evaporates faster.
Polyester also resists pilling better than most natural fibers. A polyester shirt will generally look newer longer than a cotton one washed the same number of times, because the fibers are stronger and more resistant to the friction that causes those small fabric balls. The main downside is odor. Bacteria cling to polyester more readily than to natural fibers, which is why many performance shirts include antimicrobial treatments.
Nylon: Softer and More Abrasion-Resistant
Nylon (also called polyamide) is the second most popular synthetic in athletic shirts. It’s the benchmark for strength and lightness, with higher abrasion resistance than polyester. That makes it a better choice for shirts that see heavy friction, like those worn under a backpack or climbing harness. Nylon also tends to feel softer against the skin, which is why it shows up frequently in fitted base layers and premium workout tops.
Like polyester, nylon needs special treatments to wick moisture effectively. It has slightly more natural stretch than polyester but still far less than spandex, so most nylon athletic shirts include a spandex blend for flexibility.
Spandex: The Stretch Component
Spandex (branded as Lycra) is almost never the primary fabric in an athletic shirt. Instead, it’s blended in at relatively small percentages to add flexibility. A standard moisture-wicking shirt typically contains 5 to 10% spandex for comfortable range of motion. More form-fitting performance tops use 10 to 20% spandex. Compression shirts push that to 15 to 25%, paired with 75 to 85% polyester or nylon.
Spandex can stretch five to eight times its original length without losing its shape, which is why even a small amount transforms the feel of a shirt. It’s ultra-light and doesn’t add meaningful weight, but it has low moisture-wicking ability and only medium abrasion resistance. It’s a supporting player, not the star.
Merino Wool: The Natural Alternative
Merino wool has earned a strong following in athletic apparel, particularly for hiking, trail running, and cooler-weather training. Unlike synthetic fabrics, merino is an active fiber that reacts to changes in your body temperature. In warm conditions, wool fabrics can feel up to two times cooler to the touch than synthetics because they conduct more heat away from skin. In cold conditions, wool’s natural crimp traps insulating air pockets.
The biggest advantage over synthetics is odor control. Merino fibers physically lock away odor molecules, and because wool absorbs moisture vapor rather than just transporting it along the surface, less sweat sits on your skin to breed bacteria in the first place. You can often wear a merino shirt for multiple workouts before it needs washing. Wool garments also feel less clingy than polyester when you’re sweating heavily, since the fiber absorbs moisture internally rather than holding it on the surface.
The trade-off is cost and durability. Merino shirts are typically two to three times the price of polyester equivalents, and the fibers are more prone to pilling and wear over time.
How Antimicrobial Treatments Work
Because synthetic fibers are prone to holding odor, many athletic shirts are treated with silver or zinc oxide nanoparticles embedded into the fabric structure. These metals damage bacterial cell walls on contact, preventing the colonies that produce that familiar gym-shirt smell. Zinc oxide is biocompatible and non-toxic to humans, even at neutral pH levels. Silver treatments work through a similar mechanism.
The key engineering challenge is keeping these particles from washing out. Effective treatments bond the nanoparticles into the fiber structure rather than just coating the surface, so antimicrobial performance lasts through dozens or even hundreds of wash cycles. Cheaper treatments that simply coat the exterior tend to fade quickly.
Fabric Weight and What It Means
Athletic shirts are measured in grams per square meter (GSM), and this number tells you a lot about how a shirt will feel and perform. Lightweight shirts for running, yoga, or summer training fall in the 180 to 200 GSM range. They prioritize airflow and minimal weight. Midweight performance shirts, often used for strength training or cooler conditions, sit between 210 and 250 GSM, balancing breathability with compression and support.
For comparison, a basic cotton t-shirt is usually 120 to 180 GSM. So athletic shirts are often slightly heavier than casual tees despite feeling thinner, because denser fabric construction is needed to create the capillary channels that move moisture effectively.
Recycled Polyester Performs the Same
Recycled polyester, made from post-consumer plastic bottles, is increasingly common in athletic shirts. Lab testing has shown that recycled polyester has slightly lower crystallinity and tensile strength than virgin polyester. In practice, though, this difference is undetectable. A wear trial published in the International Journal of Fashion Design found that participants could not perceive any difference between recycled and virgin polyester sports shirts across any measured attribute. If you’re choosing between two otherwise identical shirts and one uses recycled material, you’re not sacrificing performance.
How to Keep Performance Fabric Working
The single most important care rule for athletic shirts is to skip the fabric softener. Softeners leave a thin film on fibers that clogs the microscopic channels responsible for wicking moisture and allowing airflow. Over time, this coating makes performance shirts feel less breathable and more clingy, essentially undoing the engineering that makes them work.
Cold water washing and air drying are the best way to preserve stretch and antimicrobial treatments. High heat breaks down spandex fibers and can cause silver or zinc treatments to degrade faster. Synthetic fibers also pick up odors from other laundry, so washing athletic shirts separately or with similar technical fabrics helps keep them fresher longer. If a shirt has developed a persistent smell that won’t wash out, soaking it in a white vinegar solution before washing can help break down the embedded bacteria that softener buildup trapped in the fibers.