300mm scrub. Polypropylene block, filled very stiff Polyester. Wide and long surface area for maximum coverage. Removes tough surface debris. The B770 is better for spot-type cleaning on slightly less even surfaces, and for smaller areas where soiling is likely to be harder to remove. This is because the filaments will give more easily to reach dips, and there are a lot more filaments to the square inch, allowing more intense cleaning.