For those who aren't in Arizona, that appears to be Gridwall, or at least that is what some others have used. I know I can get it locally in Portland at a couple retail suppliers for reasonable prices. (2'x4' in black, white, or chrome for $17 as of today.) Sometimes it is on CL for cheaper.
Phil - what size do you use for these? I assume just the 2'x4' size, but I haven't measured, and my estimate might be off. I know you can get them in 2x4, x5, x6, x7 and x8 sizes. Do you need to trim them down?
I used 2'x4' for the attic and have a few of the other sizes.