The second programme of the 2002 Royal Institution Christmas Lectures about materials, delivered by Professor Anthony Ryan. Each lecture takes a well-known object, natural or man-made, and illustrates the amazing properties of the materials from which the object is made. In this programme, Prof Ryan discusses the modern running shoe - the trainer. "The average pair lasts just six months, but in that time, they will have run 3,000 miles, absorbed 400 litres of sweat and withstood 400 tonnes of impact. How they survive this battering is down to some miraculous chemistry that lurks beneath their flashy skin."