The Booster Strap is the essential item for improving ski boot performance. When usedÊproperly it provides for maximum boot performance and astonishing ski control, increases comfort and aids the prevention of shin bang and other boot maladies. It eliminates any empty space between the shin and the ski boot’s tongue. The stiffness varies with the different models though making variable the elastic response that has to be a choice of the skier according to his technique, morphology and skiing discipline.ÌâÊ Booster Kid is ideal for kids. Booster Soft is ideal for good skiers and light/not aggressive racers. Booster Medium is ideal for very good skiers and racers. Booster World Cup is engineered to fit the needs of the World Cup skier. Consider that it is better to begin with a softer model rather than a stiff one. How to choose: 1. Weight/Height: The Booster Medium or World cup fits Heavy/Tall athletes. Booster Soft fits Light/Short athletes. 2. Aggressiveness: Medium or World Cup fits an aggressive skier. Booster Soft fits a quiet skier. 3. Discipline: For Tech events it is suggested to ski with a Medium or World Cup, for Speed events and Freeski with the soft model. 4. Stiffness of BootsÌâ Plastics: For Stiff Boots it is suggested to ski with a Medium or World Cup, for Soft Boots with the soft model. 5. Stiffness of the Ski: For Stiff Ski it is suggested to ski with a Medium or World Cup, for Soft Ski with the soft model.