Just one #11 exacto blade for me. The trick here is to keep a sanding stone like setup by attaching 600 grit wet/dry paper to a flat block of wood etc.. While you're cutting, and the blade gets kind of dull (you know when that happens immediately) just sharpen your blade on the sandpaper. I've used the same blade cutting monokote for two complete airplanes and the blade is still in the knife. Saves lots of time and $$$$
John