GSM (Grams per Square Metre)
The weight of a fabric per square metre. The most reliable single spec for bedding density, used for sheets, towels and mattress covers where thread count is unhelpful.
GSM measures actual material weight rather than the number of threads crossing a square inch, which makes it much harder to game. Thread count can be inflated by counting plies in a twisted yarn; GSM cannot, because the fabric either weighs what it claims or it does not.
Useful benchmarks: percale sheets sit around 90–120 GSM, sateen around 120–170, flannel 150–200, and a heavyweight jersey knit 180 and up. Towels run far heavier, typically 400–700 GSM.
Higher is not automatically better. A 170 GSM sateen is denser, heavier and warmer than a 100 GSM percale, which is exactly the wrong direction for a hot sleeper. Match GSM to the season and to how warm you sleep.
For mattress covers, GSM tells you how much a quilted panel will contribute to surface feel. A heavy quilted cover adds meaningful softness above whatever foam sits beneath it.
GSM measures fabric weight in grams per square meter and is the most reliable single spec for sheets, far more so than thread count. Percale around 110-140 GSM sleeps cool and crisp; sateen at 140-180 GSM feels substantial and smooth; flannel above 170 GSM is genuinely warm.
Higher is not better, it is warmer and more opaque. A hot sleeper buying 200 GSM sateen because it sounds premium will be uncomfortable. Match GSM to your bedroom temperature first, then choose weave for feel — that ordering produces better outcomes than shopping by thread count ever does.
What This Means for Shoppers
Ignore thread-count claims above about 400 and ask for GSM instead. Hot sleepers should target the lower end of the range for their weave; anyone who wants a heavier, more draping sheet should go higher.