Orders with quantities of 299 or under units are duplicated using cd-rs. Quantities 300 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. 300 and up will be replicated DVDs and 299 and less will be on DVD-Rs.
Be sure to check out this article that speaks to the difference in manufacturing processes: