The Best media to use when copying ... uh uh I mean backing up a movie

I was reading an article on DVD Decrypter and it said

Also does dvd decryptor have software for the new dual lyer DVD burners that hold up to 8.5 GB.

Last Question some one here told me they make blank dual layer double sided Disc. Where are they I know they cost a lot but I just want to see for my self.