Hamster and gerbils are highly active pets. The Runner Medium is the ideal way to exercise your pet safely, providing fun and entertainment for you and your small friend. Directions for use: Exercise sessions should be carried out on a level floor and limited to 20 minutes per hour. Then return your pet to his cage for food, water, and rest. Remember to supervise young children and never leave your pet inside the ball in direct sunlight. Only the Runner Medium is made from high impact non-toxic polystyrene which makes the Runner Medium very robust. The Runner Mediuml requires minimal maintenance except for the occasional wash in warm water.