Performance fabric: reading a spec sheet without being fooled

The numbers that are real

gsm. Grams per square metre. The weight, the cost and the hand feel, all in one number. It is the first thing to fix and the first thing a factory will quietly reduce.

Fibre composition. A percentage, tested, not a description. Polyester with elastane at a stated percentage behaves differently from polyester with a little stretch.

Construction. Knit or woven, and the specific structure. An interlock knit and a single jersey at the same gsm are different garments.

Denier and filament count. For woven technical fabric, these describe the yarn and therefore the drape and the durability.

The claims that are mostly free

Moisture wicking is a finish and a fibre structure. It can be tested, with a defined method that measures how fast water spreads and dries. Ask for the test, not for the adjective.

Antibacterial finishes wash out, usually well before the garment does. If it matters to your market, ask for the wash-durability test at the number of washes you claim on the label.

Four-way stretch means elastane in both directions. Two-way means one. This one is easy to check with your hands.

The tests worth paying for

Martindale abrasion, for pilling. Colour fastness to washing, to rubbing and to perspiration, which is the one that catches out sports apparel. Dimensional stability after washing, which is how you find out whether the shirt shrinks a size.

Each of these is a small cost against a production run, and each of them corresponds to a specific customer complaint you will otherwise receive.

How to buy it

Name the mill. Name the fabric reference. Fix the gsm with a tolerance. Approve the bulk roll. Test the finished garment, not the fabric swatch, because the dyeing and finishing of a bulk roll is where the properties actually get decided.