Fabric sourcing for clothing brands: GSM, composition and colour

GSM: what fabric weight tells you

GSM means grams per square metre, the standard way to state the weight of knitted fabric. As a general guide, lightweight T-shirt jersey sits around 140–180 GSM, heavyweight tees start at about 220 GSM, and brushed fleece for hoodies and sweatshirts runs roughly 280–450 GSM. Wovens are often quoted the same way, though some mills use ounces per square yard.

GSM is not the same as quality. Two fabrics at 240 GSM can feel very different depending on the yarn, the knit structure and the finishing, so read the weight together with the composition and a physical swatch. Weight also shifts with washing and finishing, which is why it is measured on the actual lot rather than taken from a catalogue.

Composition and construction

Composition is the fibre content by percentage. It drives hand-feel, shrinkage, how well a print or dye takes, and what goes on the care label. Construction matters as much: jersey, piqué, rib, terry and fleece are different knits that can use the same yarn, and twill and canvas are different weaves.

• Cotton: soft and breathable; shrinks more than synthetics unless it is pre-shrunk or compacted.
• Cotton/polyester blends: more stable in the wash and less prone to shrinking; common in fleece.
• Polyester: needed for sublimation printing, which only bonds to polyester fibres; common in sportswear.
• Elastane: added in small percentages for stretch and recovery in rib and fitted garments.

Stock colours or custom-dyed

Stock fabric is what a mill already produces in its standard colours. It is usually quicker to sample from and suits smaller quantities, because there is no dyeing run to fill.

Custom-dyed fabric is dyed to your colour reference, such as a Pantone TCX code or a physical swatch. Mills dye in lots and set a minimum quantity per colour, which depends on the mill and the fabric. That dye-lot minimum is stated in the quote. If your quantity per colour is below it, you can see that up front and choose between meeting the minimum and using a close stock colour.

Lab dips: approving a colour before bulk dyeing

A lab dip is a small piece of your fabric dyed to your colour reference before the mill dyes the bulk. Usually several variants are dyed side by side, and you pick the closest or ask for another round. The general sequence:

1. You send the colour reference: a Pantone TCX code, a physical swatch or a previously approved fabric.
2. The dips are made on the actual base fabric, because the same dye looks different on cotton and on polyester.
3. You compare them under a stated light source, usually D65 daylight, since colours can shift between lights.
4. The approved dip becomes the shade standard each bulk dye lot is checked against before cutting.