Grammage (g/m², GSM)
The weight in grams of one square metre of paper, board, fabric, nonwoven or film (ISO 536, ISO 3801). Typical values: newsprint 40–48, office paper 70–80, kraftliner and fluting 100–440 g/m²; T-shirt jersey 140–200 and denim 300–450 g/m²; a face-mask meltblown layer 20–25 g/m². Grammage drives price and strength directly but is not enough on its own: specifications should also include burst (Mullen), ring crush (RCT) and edge crush (ECT) for board, and tensile and pilling resistance for fabric.
Related terms
Yarn count (Ne, Nm, tex, dtex, denier)
Measures of yarn fineness, in two systems. In indirect systems a higher number means a finer yarn: Ne for cotton (hanks of 840 yards per pound; Ne 30 is a typical T-shirt yarn) and Nm for wool (metres per gram). In direct systems a higher number means a coarser yarn: tex (grams per 1,000 m), dtex (per 10,000 m) and, for synthetic filament, denier (per 9,000 m – e.g. 150D/48F polyester DTY is 150 denier with 48 filaments). Twist, tenacity and evenness (Uster CV%) also define quality.
Recovered paper grades (EN 643, OCC 11, ONP, SOP)
Recovered paper and board are classed under the European EN 643 list – e.g. 1.04 supermarket corrugated, 1.05 old corrugated containers – and in US and international trade under ISRI/ReMA codes: OCC 11 (old corrugated containers with kraft liners), DLK (double-lined kraft cuttings), ONP (old newspapers) and SOP/WL (white office paper). Besides fibre quality, price depends on moisture (usually 10–12 % maximum) and unwanted material – plastic, metal, wet-strength paper, known as outthrows and prohibitives. Import restrictions in China and elsewhere have tightened cleanliness standards.