Orders with quantities of 499 or under units are duplicated using cd-rs.
Quantities 500 or more are replicated using CDs.
The online quoter will change the type of manufacturing based upon the quantity that you enter.
The same applies to DVD-Rs and DVDs. 500 and up will be replicated DVDs and 499 and less will be on DVD-Rs.
Be sure to check out this article that speaks to the difference in manufacturing processes: