The K2 Mindbender 100 boot has a flex rating of 100. Adult Ski boot flex ratings range from 65 to 130+, and a flex rating of 100 indicates a medium-flexing boot. , The flex rating of the K2 Ski Mindbender 100 is 100. The touring boot is a medium volume ideal for intermediate to advanced skiers looking to dip their toes into the backcountry realm. The medium flex rating of 100 will give the skier plenty of stiffness for response but just enough flex to keep them coming back into the backcountry. , The K2 Mindbender 100 boot has a flex index rating of 100 as detailed in its name. The number following the boot name generally relates to the flex index of the boot.