There are three factors used to differentiate the styles: stretch, durability, and activity level.
Stretch is defined by the materials used in each pant where some made with fabrics that have a lot of stretch like a nylon/spandex combination. Stretch is also defined by the cut and fit that can be optimized for wider range of motion.
With the durability factor, we know that all Härkila’s clothes are always made to last, but some of our pants are made to withstand the extremely rough thicket where activities like terrain maintenance take place. Reinforced panels and choice of material determines the durability scale where materials like our waxed hardwearing canvas are the highest level of the scale.