The Carlisle 4042514 Spectrum Boot 'N Shoe brush replacement with blue bristles works with a Carlisle 4042403 brush (sold separately) to help remove, refuse, dirt, and other debris from boots and shoes before entering sensitive sites, such as food processing areas. The bristles are made of polypropylene for durability and extended life. The brush is free of BPA (Bisphenol A). The block dimensions are 10 x 4-1/2 x 3-1/2 inches (L x W x H).