Double layer +r discs are down to anout £2 each now, the double layer -r are new so diffcult to find. I always use single layer -r discs as they are compatable with more dvd players than +r, unless you set booktype on them to dvd rom. But not all writers can change the booktype. The only advantage with double layer is that you can back up a dvd9 movie without compressing it or removing any extras, also some xbox games are dvd9 although most can be ripped to dvd5. another good site is www.cdfreaks.com