I purchased a few of these glow in the dark balls so that my boys could find their ball when they play street hockey after dark. They find that it's made a difference since in winter it tends to get darker faster and now they can find the ball especially if it gets under cars or some other nook and cranny. Now they glow in the dark and are easy to spot. It actually states on the packaging that it's a low density ball for cool weather. The ball changes colour depending on the temperature. Quite a cool feature!