I have detailed DIY designs for three types of RPG-style diffusors which I'd be glad to email you. I used 1/2" medite for the first and have used Styrofoam (which does a fair amount of absorbing along with diffusing, more or less like RPG's Abffusor) after that, for lighter weight, easier construction. But any board could be used. My clones of RPG's Skyline work as well as the real thing, as far as I can tell. But then all my models are sure to work--the basic design behind them is precisely the same as RPG's. A little of the theory can be found in F. Alton Everest's "Sound Studio Construction on a Budget", maybe also in his "Master Handbook of Acoustics", but be sure to get the 4th edition. Jon Risch has detailed instructions for tube traps a la ASC but the construction looks a lot messier than my DIY projects--which do, however, call for a table saw or the like to cut the pieces. Good luck!