Virgil.
¯\(°_o)/¯
Kinda, these portable absorbers - and basically every other acoustic treatment - were planned and designed by an acoustician/studio-designer: http://www.mikasmietshaus.de/ He's called "Mikas Mietshaus" on the forum and posted a few times in this thread.
I can't hand out the plans unfortunately.
If you look through the thread, there are pictures of the construction process of those absorbers and from there you should be able to clone them
The absorber is filled with 10cm deep Isover mineral wool called TP1, the names and Isover products are different for the US and Europe, though.
The fabric is called "Molton" or "Bühnen-Molton" (stage molton?). Not sure how it's called in english really, I only find the word and wikipedia entries in french, danish and some other European languages It's the fabric that gets used in theaters, cinemas and studios a lot, made out of 100% cotton and napped on both sides of the fabric. Canvas is often used for acoustic panels too, but I don't like the look honestly.
Cool, thanks for the information!