Reply by John

It depends on what you’re sanding. Ideally, the shape of the sanding pad matches the shape of your work. If you’re sanding a flat surface, a hard, flat sanding block is good. It also allows you to use it sort of like a block plane and make faceted edges vs. a softer block which will round off corners. A hard backing also allows you to put more pressure and really hog off material with a coarse grade of sandpaper.

I use firm rubber pads for a lot of tasks, and my shopmade wood blocks for others. I don’t bother with any backing on the wood blocks.