Subject: Material of microwave oven walls?

I would like to know the material out of which the walls of 
microwave ovens are made after looking at all the different 
problems posted about the behaviour of metals in microwave 
ovens.  Is there any special treatment for the materials used?
Also, how is the oven made leak-proof?  Doesn't the wall 
material heat up?  I have investigated the glass door (does not 
heat up) and some of the front rods inside (does heat up), but 
how about the walls (my hand never reached that far).  And how 
would you think different materials would act, like metals, 
plastcs, ceramics, composites...
Thank you.

Re: Material of microwave oven walls?