Plywoods and MDF come in all different price ranges and grades.  The
MDF from the "big box stores", as someone called them, is basically
used for floor underlayment.  It's meant to be screwed down as a
substrate -- _nothing more!_  If you have the desire to use MDF, try
finding a wholesaler that supplies cabinet shops.  Ultra-light MDF,
though costing a few cents more than the standard MDF, weighs 1/2 as
much.

A new product on the market is a plywood substrate, with an 1/8" skin
on both side of MDF.  The purpose is to supply a light weight product,
with a bit more strength, but it will finish nicer than plywood, when
painting.  As I mentioned before, there is also a water resistant MDF
and a waterproof or exterior MDF.

The Baltic birchs (plywood) offer a product with more layers than the
standard plywoods, of course at a bit more cost.  If its strength you
are looking for, lumbercore is still available.  That would be strips
of solid lumber glued together, with a veneer skin, face and back.

When left alone, I would say that the MDF is the most stable product,
but all of them would warp if you were to finish one side and left
the backside raw.

As for gluing bellows cloth to the edge, you might want to glue size
the edges, and after it dries, sand it with a 220 grit paper, then try
the hide glue.  And as for screwing into the edges, try rabbiting in
a solid piece of solid lumber, or use a mitered joint with a spline.

Howard Jensen
New York