Polyurethane Shoe Sole Waste

These rubbery monochrome mounds may be reminiscent of either stalagmites or Cousin Itt from the Addams Family, but they are in fact waste polyurethane foam that has dripped off a high-speed shoe sole manufacturing line in Lancashire. They were collected by our Director Zoe at the Hotter shoe factory during the filming of her BBC How to Make series, in the Trainers episode.

In this episode Zoe explores the history of shoe sole materials and searches for the perfect material with which to make her own pair of trainers. In the process, she visits a shoe factory floor to witness the moment when isocyanate, polyol and water come together at high speed to form a polyurethane foam shoe sole that is injection moulded directly onto the base of the shoe, taking just nine seconds per shoe. The mix of chemicals creates an expanding, exothermic, self-skinning foam that quickly grows to fill the aluminium mould, creating a squidy and glossy tread that picks up all the detail of the mould. The shoe is then removed from the mould with its sole attached, and a small amount of flashing is trimmed off by hand before the shoe is ready to be packaged and sold.