If you cut the vertical posts in a triangular shape, instead of squares like mine, you will be able to have a flat surface facing the room.

The material is "OC-703 foil reinforced". I can't recall exactly where I got the cue about the foil, it's been a while, but I read all I could find on the subject and the membrane effect is well-documented. Try googling something along the lines of "corner bass traps + membrane effect + OC-703 foil + low frequencies" and you should find some information.

Cheers,

Dramis