These discs are typically made of compressed wool felt, offering a soft, elastic, and wear-resistant material for polishing various surfaces. 

They are commonly used with angle grinders for tasks like polishing metal, glass, ceramics, marble, and even car surfaces. 

The discs are designed to produce a smooth and bright finish, effectively eliminating traces and brightening the polished item. 

They come in various sizes, with common diameters around 100mm and bore sizes around 16mm to fit standard angle grinders.