From Vitra’s youtube channel:
Tip Ton defines the new design standard for the forward-tiltable all-plastic chair: it can be tilted forward from its normal position and will remain stationary at a 9 degree incline. This forward-slanted sitting position, which has only been available to date from sophisticated office chairs, straightens the pelvis and spine thereby improving circulation through the stomach and back muscles. Up to four Tip Ton chairs can be stacked on one another and the chair is available in eight different colours. It is made from polypropylene, is extremely durable and 100% recyclable.