Not all balls are created equal!
The DuraBall Pro Swiss Ball is tested in a specially designed apparatus, which can progressively load a ball with a series of free weight. The test ball is then punctured with a very sharp, 10mm knife blade. A ball is deemed to be anti burst when the cut in the ball does not expand from the size of the cut made by the blade. The manufacturer's tests on the DuraBall Pro have exceeded a 500kg burst resistance rating. This means that if you applied a dynamic load of 500kg to the ball and it suffered a puncture of any kind, it will deflate slowly. This gives a margin of safety to prevent injury in any use of the ball.
Our word of advice on this is that where ever there is an element of risk of injury when a ball should spontaneously disappear out from under the user - specify an anti-burst nature ball. Always use an anti-burst ball with free weights.
DuraBall Sizing