Use the balsa side with low-grit sandpaper for hard sanding, like squaring up rails or working down the stringer. Use the soft foam pad side with various grits sandpaper smoothing out bumps and blending. The block is made of balsa wood and foam. Dimensions: 4" x 11".
For use with 9" x 11" Sandpaper Sheets.
"Quality Surfboard Shaping Tools & Materials"