What does GSM mean for fleece and how do I pick the right weight?

GSM means grams per square metre — the density and weight of the fabric. Higher GSM generally means a warmer, thicker, slower-drying fleece; lower GSM means lighter weight and better packability.

Practical bands for fleece programmes: 100–150 GSM microfleece for active base or lining; 150–300 GSM midweight, the standard choice for midlayers worn over a base layer; 300+ GSM heavyweight for static warmth around camp or as outerlayers in cold, dry conditions. For a hiking brand, start at 200–280 GSM for the core midlayer SKU, then extend light or heavy variants once the line proves out.