How to read a luxury swimwear fabric label

Most swimwear labels list a fibre content and not much else. A typical label might say 80% polyamide, 20% elastane, and leave you to work out whether that means the fabric will last one holiday or five. The difference between swimwear that holds its shape and swimwear that does not is almost always in the fabric construction and the grade of elastane used, neither of which appears on the label.

Polyamide versus polyester as the base fibre ¶

Swimwear fabrics use either polyamide (nylon) or polyester as the base fibre. Polyamide is softer against the skin and has a slightly higher stretch recovery, which is why most luxury swimwear uses it. Polyester is more resistant to UV degradation and is common in performance sportswear, but it tends to feel stiffer and is harder to dye to deep, saturated colours.

The percentage of polyamide in the fabric matters less than the grade. A high-grade polyamide yarn produces a smoother, denser fabric with a better hand feel. A lower-grade yarn produces a fabric that looks similar on a hanger but pills faster and loses its surface finish after repeated washing.

What the elastane percentage tells you ¶

Elastane (sold under brand names including Lycra) is the fibre that gives swimwear its stretch. A fabric with 18 to 22 percent elastane has good stretch and recovery for most swimwear applications. Above 25 percent, the fabric becomes very stretchy but also more vulnerable to chlorine degradation, because there is more elastane for the chlorine to attack.

Chlorine-resistant elastane variants exist and are used in higher-quality swimwear fabrics. They are not labelled differently on the garment, which is one reason fabric sourcing from known mills matters. A fabric from a mill that tests for chlorine resistance is a different product from a fabric with the same fibre content from a mill that does not.

Single-knit versus double-knit construction ¶

The knit structure of the fabric affects opacity, weight, and how the garment holds its shape under tension. A single-knit fabric is lighter and more transparent, particularly when wet or stretched. A double-knit fabric is denser, more opaque, and holds its shape better under the stress of movement.

For structured swimwear with underwire boning, a double-knit fabric is the appropriate choice. The denser structure distributes the tension from the boning more evenly and resists the distortion that a single-knit fabric develops around underwire channels over time.

Reading a fabric label will not tell you everything, but knowing what to look for narrows the field considerably. The construction details are worth asking about before you buy.