I'm sure you have at least one pair of old, worn down shoes that you don't know what to do with. Goodwill won't accept them because they're too beaten up and you can't give them away because they're just too unseemly. Just give it to Nike's Reuse-A-Shoe recycling bins. Nike will mix them in with a raw material called Nike Grind. It's used in paving tracks and making soles. Turning something old and beaten up into something new and useful.