It depends on you plan to use them.
I made mine closed back to be able to use them as reflector.. (my recording room is pretty dead so it gives me some options)

For the gobos to be functional as intended fabric in the front soft side if nothing else it hides the insulation. But using a hardboard on the opposite side is always good so you can bring back some high frequency if needed and I would cover it with light breathable fabric...but that would just be my preferance.

So it begins! :)

@Brien Holcombe , thanks for the advice, I got felt for the front and hardboard for the back.

I built this bi-fold gobo - results are posted as a continuation of this discussion, from another thread.

Minor update for the heck of it: I built a desktop version of this bi-fold gobo. It works surprisingly well!

[MEDIA=audio]https://recording.o…