Tom,
I believe that the MDF he refers to stands for medium density fiberboard. It is like a very hard compressed cardboard. Considerable dust when you cut it. Not very strong, but rigid enough for hobby stuff. I think you can go to Lowe's or Home Depot and look at a sheet of it. If it gets wet, it swells and never really dries back to its original thickness or shape. If it gets too wet, it dissolves. If you have ever looked at the super cheap furniture that is being sold in places like WalMart, the flat surfaces are often MDF with a layer of thin vinyl veneer stuck on top of it. You often see it used as the bottom section of a pull out drawer. I think when you go see it, you will recognize it. It bends fairly easily.
Mannyrock
