[Lefatshe]

Look at how wonderful these cardboard forms would be as a diffuser!!!  My wife just received a shipment from Nakedwines.com and this is how they hold the bottles in the box.

[JLM]

The material doesn't 'look' acoustically opaque so they wouldn't offer much of a barrier to sound traveling through it and therefore not provide significant diffusion.  Plus they aren't random depths, so would only diffuse at one frequency (approximately 1600 Hz from my guess of about 4 inch depth). 

Here's a link to plans for a much better inexpensive (but heavy) diffuser:

http://www.pmerecords.com/Diffusor.cfm

[gab]

or here:

http://www.oliverprime.com/prd/?show=calculator

http://www.diyaudio.com/forums/construction-tips/269366-easy-diy-depot-sound-diffuser-panels-step-step.html

http://www.mh-audio.nl/DiffusorCalculator3.asp?km=3.56&kl=30.48&calc=Calculate+Diffuser#result