Abrasha Photography Setup

To Mr. Abrasha:

I viewed your website at www.abrasha.com/misc/photoraphy.htm and was
impressed with the simplicity and ingenuity of your photography
setup…However, I was unclear as to the type of material used in the
sides (called translucent colorless gels) and where to obtain it.
Also, I could not discern exactly how the sloping gray paper was
placed inside the photo box.

Would appreciate your help.