Nova exercise balls are an expertly designed set of three different exercise balls to perform kegel ball exercises with. Each ball is equipped with a silicone string to easily take out the ball after use. The entire Nova ball is made of body-safe silicone which is 100% waterproof. According to the kegel exercis e theory, we designed these kegel exercise courses especially to help those who want to tighten their vagina mucles after giving birth. The set of Nova balls have three gradual increased weights for different exercise needs. Effective kegel exercise helps to strengthen a woman' s PC muscle (pubococcygeus muscle), improving vaginal health while bringing sexual benefits and satisfaction. For daily exercise or postpartum recovery, Nova exercise balls are the perfect choice for your PC muscle strengthening needs.