Hard-bristle brushes are designed for the mechanical removal of stubborn and dried-on dirt. The bristles are made from robust synthetic materials that can handle, for example, mud, moss, or deposits on hard and less sensitive surfaces. They are therefore suitable for cleaning tiles, stone, concrete, or durable metal structures. Conversely, they are not recommended for use on sensitive materials such as car paint, glass, or soft wood, as they could cause scratching.