More brands now print a number next to the fabric: 230gsm, 450gsm, 620gsm. It is the single most useful thing on a product page, and the least explained. Here is what it means.
What GSM is
GSM stands for grams per square metre: the weight of one square metre of the fabric. A higher number means a denser, heavier cloth. Mills measure it by cutting a circle of exactly 100 square centimetres, weighing it and multiplying by 100. American labels often use ounces per square yard instead; one ounce per square yard is about 34gsm.
What counts as heavyweight
There is no official standard, only conventions. Roughly:
- Under 150gsm: lightweight. Most multipack and promotional tees.
- 150–200gsm: the everyday tee.
- 200–250gsm: midweight. Holds its shape and does not go see-through.
- 250gsm and up: heavyweight. Structured, with a dense, dry hand.
Sweatshirt fabrics start higher: 300–400gsm is a normal crewneck, and anything above 450gsm is heavy.
What we use
- Tees and women's tees: 230gsm midweight cotton
- Long-sleeve tees: 250gsm cotton jersey
- Crop tees: 200gsm cotton
- Crewnecks: 450gsm cotton French terry
- Hoodies, quarter-zips and sweatpants: 620gsm bonded French terry
We call the tees midweight because they are. They are heavy enough to hold a boxy shape and wear well under a shell, and light enough to be comfortable on a terrace in March.
What matters besides weight
The yarn
Combed cotton has had its short fibres removed, leaving long parallel ones that make a smoother, more lustrous yarn. Ring-spun yarn is stronger than the cheaper open-end kind. Weight tells you how much cotton there is; the yarn tells you how good it is.
The knit
Tees are single jersey. Sweatshirts are usually French terry, which is smooth on the face and looped on the inside, or fleece, where those loops are brushed until they go fluffy. Terry is smoother and keeps its shape; fleece feels warmer and softer.
The cut
A heavy fabric in a bad cut is still a bad tee. Ours are boxy with dropped shoulders, so the weight hangs straight rather than clinging.
How to look after it
Research by Cotton Incorporated found that it is the tumbling in a dryer, more than the heat, that shrinks cotton. So wash cold, inside out, with similar colours, and line dry. Do not iron over the print. Heavy cotton treated this way softens with wear and holds its size far better.