Low quality exercise balls do not give you a good workout, can burst suddenly under pressure and may have to be replaced soon after purchase. If you are in the market for an exercise ball, here are some important guidelines on how to buy a good one: first, look closely at the material. If the ball feels slick and thin and has a strong plastic smell, it is not likely to sustain much weight and could pop easily under pressure. High quality balls are made of burst-resistant vinyl and are independently tested to withstand as much as 600 pounds while still retaining their shape and usefulness. Second, read the package carefully to be certain that if the ball is punctured, it will not drop you to the ground like a hot potato. High quality balls are designed to deflate slowly if punctured to minimize the risk of injury. Lastly, do not forget to inflate it to the right height and use it properly - for safety reasons and to ensure maximum workout results.