Mine's architect's drafting paper (similar to parchment or non-reflective wax paper in appearance). It softens the flash wonderfully, and you don't loose very much light to it. It's REALLY cheap–Ihold mine on with a rubber band. A tad tacky, but very nice output.
I've been using the Lightsphere II and like it. I just ordered a Lightsphere PJ to see if it is any good. From what has been posted, the LSII is a bit more warm than the PJ. Other than the size, I like the LSII.