The medium is called Leca and they are clay balls that are part of a semi-hydroponic system that is available
A Hydroculture Oasis. I grow all of my orchids in this type of culture and have had excellent results. It's a little pricey to begin with, but they were much less trouble to tend to once they got started. If yo check out that site, or go to the Semi-Hydroponic section of this board, I'm sure you can get all the information that you need. Good luck with your growing!