The first reloading bench I built - at age 17 - used a 5/8 thick piece of plywood as a structural component of the bench. The second reloading bench I built - at age 27, after I had collected a sheaf of engineering degrees - used a 7/16 thick piece of waferboard. And this was only because I couldn't get anything thinner (cheaper). Once I had been trained in how to resist and transmit forces, the top of the bench became an irrelevancy. As far as I am concerned, the structure of a properly designed and built reloading bench should harness and transmit all the forces to the ground; the bench top should exist for no other reason than to keep reloading components off the floor.