What does GSM mean in fabric?
Grams per square meter - fabric weight. Higher GSM means thicker, more durable fabric; for tees, 180-220 is the quality zone.
GSM tells you how much fabric you are actually getting. T-shirts run 120-220 GSM: below 150 is thin and drapes into transparency fast; 180-220 is the substantial, holds-its-shape range of good heavyweight tees. Hoodies live at 300-400. Towels at 500-700. GSM is not a quality guarantee - a heavy fabric of short-staple cotton still pills - but a suspiciously low number is a reliable warning. When brands do not list GSM for basics, the usual reason is that the number would embarrass them. For dress shirts look instead at thread count and ply (two-ply is the mark of a shirt that lasts).