MDF is not used on pipe organ construction for many reasons, but the
most notable, after esthetics, is that each organ pipe is scaled to the
pipes above and below it.  This is both in width versus speaking length
and in pipe wall thickness.  You cannot plane down MDF to keep the pipe
wall thickness in the same ratio to pipe width as you would do with
naturally grown wood.

The preferred wood for pipe organ pipes is sugar pine (pinus
lambertiana) though some of the finest pipework in the world was done
in redwood (Sequoia sempervirons) by Murray Harris.  The close fine
grain of natural wood lets you use your planer to customize each of the
pipe wall thickness.  For short compass faire organs and the like this
would probably not be a great issue.

However, while the Dutch study and others done here in the United
States have shown that pipe material is somewhat inconsequential,
the standing wave within the pipe resonator body is effected by the
rigidity and porosity of the pipe walls.  A normal wood pipe is "sized"
with hot glue inside to seal the wood.

At approximately halfway up the resonator of an open flue pipe you will
find the nodal point or node, an area with little molecular movement in
the standing wave.  Most people interpret that this means the nodal
point is non-critical, nothing could be further from the truth.  The
node may be an area of no wave motion but it is the area of maximum
pressure changes within the wave.

If you could lay a pipe on its side and supply wind to get oscillation
going, then throw in some cork dust, you would see the cork dust at
the node form a line where the pressure fronts from both sides of the
standing wave push the cork particles together.  This means that the
walls in the node are critical.

A well constructed pipe of natural grain wood will allow the walls to
flex imperceptibly.  The result is that the pipe will have a slightly
more live tone from harmonics that result.  The stiffness of MDF would
likely dampen the wall oscillation.  Well designed pipe organ pipes do
take into account wall thickness that are graduated with scale for
precisely this reason.

Al Sefl, Ph.D.