I just used burlap but am unimaginative and did not test any other fabric. There may be less expensive, more-fit-for-purpose fabrics for all I know. Burlap isn't necessarily expensive, but if you buy enough burlap then it ain't cheap either. My "minimal materials count" absorber projects probably spent as much money on burlap as on wood framing or the pink fluffy or safe'n'sound mineral wool. IOW, especially with cheap big pink fluffy bass traps, maybe the cost got equally spread between wood, insulation and burlap. I asked the fabric store lady about it. She said that nowadays big fancy weddings buy lots and lots of burlap for decorative purposes in the ceremony or reception. Too arty for me. When I was a kid they used burlap for feed sacks and cotton-picking bags.
If you need to be fire-rated then burlap or other non-fire-rated fabric needs spraying with commercial or homemade gunk to make it fire-******ant. Dang I don't know why this forum always spells
****** with asterisks. I suppose
Fire ******ation is somehow politically incorrect. Maybe
"Fire Special Needs" is a more desirable and accurate engineering terminology!
I didn't bother with that. If the office catches fire when I'm in there then I'll just have to be either quick or dead. However the space is for personal use so it is unlikely that there will be numerous dumb customers hanging out who need to be shooed out like cows from a barn if the office catches fire.
My burlap faced absorbers are 2 or 3 years old and none of the fabric has shown signs of sagging. Maybe tomorrow they will all decide to sag all at once, but so far they remain tight as a drum.
Maybe because I have a somewhat obsessive compulsive, belt-and-suspenders personality. I routinely twist the heads off bolts making sure that they are tight enough.
I would stretch the burlap real tight using about 1 staple per inch. Electric staple gun staples are cheap and the finger doesn't get sore pressing the trigger. Then I glued down each seam where the burlap touches a wood frame edge.
At first I used Titebond III wood glue to glue down the seams. The titebond III works great but turns brown after it dries. So it is ugly as sin unless all seams and glue drippings are covered by decorative wood strips.
Then I discovered an adhesive easy available in USA (dunno other countries) Loktite Power Grab. It comes in caulk gun tubes and several formulations, though the cheapest interior-use version seems to work fine for burlap. It dries fast and completely clear, but so far as I can tell seems "chemically in the same family" as good aliphatic glues such as Titebond.
I would staple all the burlap on an absorber, then run a bead of Titebond or Power Grab down each wood strut. Then take finger and "rub in" the glue so it soaks into the burlap fibers and underlying wood. After about an hour of drying, all the burlap fibers are glued so good to the wood frame that you could pull all the staples and the fabric would remain tight in place.