Pascal Schmidt wrote in a message to Roy J. Tellason:

 PS> Hi Roy! :-)

 RJT> I can understand getting into trouble with those if you leave them 
 RJT> laying in direct sunlight,  but I am having a bit of difficulty with 
 RJT> the dampness part,  though I've heard of those problems too.  You'd 
 RJT> think that plastic would be sealed from any moisture entering.  

 PS> I don't think a writable CD, where the layer that actually carries
 PS> the data is usually made from organic material, is sealed in
 PS> plastic on the edge. I think they just put layer on layer during
 PS> production, so the plastic part protects the flat surface, but not
 PS> the edges. Most discs I have seen gone bad started to come apart or
 PS> wither away from the outside.

How odd,  that they'd make them that way.

 RJT> Though maybe it's chosen first for its optical qualities and 
 RJT> secondly for any other characteristics...

 PS> Yeah, it has to have the right optical qualities for being able to
 PS> read and write it via laser beam (which implies it has to be
 PS> somewhat heat-resistent). 

Or at least transparent at the wavelengths involved.

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