Bristles are for finer particles and blades scoop in larger pieces, but both work together to clean the floor. The materials they’re made of differ, machine to machine. Blades are usually made of rubber or another soft but strong material that won’t scratch hardwood or carpet. Man-made and natural materials are both used to make bristles. Man-made might last longer, but some buyers would prefer to use less plastic and worry these bristles will be too coarse for their sensitive floor surfaces. Natural materials might raise issues about animal testing.