To provide an indication of boot rigidity, brands assign a flex rating to every boot. This figure indicates the rigidity of the boot: the higher its value, the stiffer the shell. A flex of 60 to 70 is considered best for skiers at beginner level. A flex from 70 to 100 is for intermediate skiers. Beyond this value, the products are aimed at advanced skiers. Heavy builds can, however, go up a level.