92% Polyamide & 8% Stretch. Polyamide is durable, strong, dimensionally stable, wrinkle-free and flexible. Durable because the fabric is strong, and therefore wears little and therefore lasts a long time.
The model in the photo is 64 kilos and wears size S. However, the fabric is tighter because it is a bit thicker. So would you rather have your leggings fall a little looser and higher in your waist? Then take a size bigger.