GSM stands for grams per square metre. The higher the number, the denser the fabric.
A regular tee sits around 160–180 GSM. Heavyweight tees start around 220 GSM; ours are 240.
More weight means better drape, less see-through, and a boxy shape that holds up wash after wash.
The trade-off: heavyweight cotton is warmer, so it's perfect for Kathmandu's cooler months and layering.