why framing and conservation is expensive (and important)

in short, it's both the materials required and time

http://www.vimeo.com/11712163

There is a difference between materials tested by time and materials tested by accelerated time tests.
100% cotton is best for both backings and also as substances on which the art is printed.
"Buffered" boards are only effective for a couple of years. The buffering wears out quickly.
Plexiglass is more stable than aluminum, and less likely to break than glass.