Icebug Insoles with Arch Flex System Technology support the foot's entire structure and provide an energy return with every step. The Insoles react like a stability ball, providing dynamic support. Icebug Insoles respond to your body type and activity, keeping your feet healthy,energized, and comfortable. These insoles adress the three arches of the foot: Medial, Lateral, and Metatarsal. Fat and Slim refer to the thickness of the Insole: The Slim Insole is best for those looking for an insole with modest cushioning. This type of insole fits best in footwear with a non-removable existing footbed. Low, Medium, and High refer to the arch height/shape of the user: The Low Insole is best suited for those with a lower arch height (flatter feet).