What is "crumb rubber"

n. A form of recycled rubber with a granular consistency, generally from tyres after the removal of steel etc.

Crumb rubber is recycled rubber produced from automotive and truck scrap tires. During the recycling process, steel and tire cord (fluff) are removed, leaving tire rubber with a granular consistency. Continued processing with a granulator or cracker mill, possibly with the aid of cryogenics or by mechanical means, reduces the size of the particles further. The particles are sized and classified based on various criteria including color (black only or black and white). The granulate is sized by passing through a screen, the size based on a dimension (1/4 inch) or mesh (holes per inch : 10, 20, etc.). Crumb rubber is often used in astroturf as cushioning, where it is sometimes referred to as astro-dirt.