The Reebok Elements gym ball has an anti-burst design with features ribbing for additional grip. It is 65cm (25.6") in diameter and a maximum user weight of 110kg (242.5lbs). This cyan gym ball offers excellent balance between support and instability and can be used for improving core stability and strength. Please note that when you blow the ball up for the first time, you should do it only up to 80% of the correct size and leave it overnight to allow the fibres to 'stabilise'. On the next day add the remaining 20%. In this way you will make the surface of the ball smooth and most stable.