Whether you call it a stability ball, a Swiss ball, a yoga ball, or a birthing ball, a quality exercise ball should support the weight of your moving body, retain air, and deflate slowly if punctured. After spending 30 hours doing research, plus nearly two hours inflating seven top contenders from the more than 80 models we considered, we’ve found that the TheraBand Pro Series SCP Exercise Ball is the best exercise ball for most people. It’s made of sturdy yet flexible plastic that, when properly inflated, tied for the most-supportive seat among all the models we tested, and its plug provided the tightest seal.