[AaronInCarolina]

Well I have some from the 80's that are still good as new and work just fine so at least 20+ years.

I suspect you are referring to commercially-created CD's, not the less reliable home-burned CD's. I think the issue is that the home-burners don't create discs that are as reliable long-term as the commercially-produced discs.

[Petronski]

You're correct. Commercial CDs are stamped in an aluminum substrate. CD-Rs are burned onto a layer of reactive dye (think of the old, curly thermal fax paper).