Use these Exercise Balls for sitting, standing or lying exercises. Ideal for stretching and working to improve posture, balance, agility and strength.  Balls are made of nonslip, heavy-duty vinyl and will support up to 550 lbs.  Balls are anti-burst and will deflate slowly if punctured.  Each Exercise Ball comes with a pump, plug remover, measuring tape and illustrated exercise poster.  Clean with soapy water or disinfectant.  Latex free.  See the chart for sizing information.  Size is based on the user being in seated position with hips and knees bent at 90 degrees when seated on the ball.  If between sizes, choose the larger size.