medium reinforcement for your boot . the deeluxe flex booster 1k strengthens your boot when you need it and also ensures longer life.want to use your jib boot for a kicker session, or need a slightly stiffer flex in the backcountry? the flex booster remedies this without you having to change your boot.2k boosterthanks to its slightly harder flex, the flex booster 2k gives the boot a lot of support and response. this way you can make your boot harder by 2 points on the flex rate.