I use high density polystyrene. I first came on this material doing an audio installation the the Corvette factory. They use it instead of wood to ship engines and transmissions. It is very tough and durable. I have the best rates available worked out through Conway Freight, one of the largest in the nation. It is all based on weight, I am shipping the unit shown plus 2 diffusors that are 4 ft by 3 ft by 8.5" to central NJ for around $300.00. I can tell you that this diffusor is in the size range that REALLY starts to work in a small room. I know because I have built them all, that is all the ones listed in my website, which is an extensive list, and put them up and tried them. Basically, the bigger they are, the better they work. These units are what brings excitement to the world of audio and acoustics.
