These are a workhorse for polishing. Softer than wood or phenolics but harder than felt. Leather wheels give you a variety of options depending on your polishing needs with different textures, diameters, and thicknesses available.
1/4" thick in either 1" or 1 1/8" diameters are made of a Hard Sole Leather that can be shaped to fit your needs (Knife Edge, Square, Bevel, and the standard Round).
1/8" thick in either 1" or 1 1/8" diameters are made of a medium stiffness leather (think belt leather) which are slightly softer and conform to your carving to work fast in the polishing steps.