Both nylon and polyester are synthetic fibres, and both are knitted with elastane for leggings. The difference is in the fibre and in how it is dyed and finished. As a general rule, nylon knits tend to feel softer and smoother and are often used for a premium hand feel. Polyester knits tend to dry faster, resist light fading well and cost less. These are general tendencies, and the finished fabric depends on yarn, knit, weight and finishing, so treat them as questions to test, not as facts about your fabric.

Feel and look

Nylon is often chosen for a soft, buttery feel and a slight sheen. Polyester can feel crisper or, with fine microfibre yarns and brushing, very soft. Compare finished fabric samples against each other under the same light, and ask for the weight and knit structure of each, since a heavier polyester can feel more substantial than a light nylon.

Moisture and drying

Nylon generally takes up more moisture than polyester, which is one reason polyester is popular for sweat-heavy workouts and quick-drying. If you make a quick-dry or moisture-wicking claim, test the actual fabric rather than relying on the fibre name.

Durability and pilling

Pilling and abrasion depend on yarn type, knit and finishing. Ask for pilling results on washed fabric using a method such as ISO 12945-2 or ASTM D4970, both of which use the Martindale approach. Leggings rub at the inner thighs, so request a test that reflects that wear.

Colour and light

Both fibres can be dyed deep colours. Ask for colour fastness to light with ISO 105-B02 if the leggings will be worn outdoors, and fastness to washing and rubbing for dark shades. Check stretch and recovery with ASTM D4964 or the method your lab recommends, after washing.

Cost and the label

Nylon fabrics usually cost more. If the premium feel supports a higher retail price, it can be worth it, but check that buyers notice the difference. Whatever you choose, state the fibres by their generic names, nylon or polyester, and elastane or spandex, on the label in line with the FTC rules at 16 CFR Part 303.

Ask each supplier for a washed sample and test results before you decide.