Three sanding blocks will be needed in order to ensure a straight, sleek, and smooth finish during the blocking process. One is a conventional hard block, perfect for cutting flat surfaces to create a straight finish. Second, is a medium based block, which too can be used for flat surfaces, but it is much more forgiving when blocking mild radiuses. Lastly, a sponge block is needed. The sponge block isn't aggressive enough to flat-spot curves, yet just aggressive enough to keep a straight finish without leaving behind trails of fingerprints.