I have been told that burlap is the best thing to use to cover 703
type board that is being used for bass traps or other exposed
treatment. The board will NOT be built into any wood frame or other
enclosure, it will be hung 4" off the wall by itself - so I'm looking
for a cloth to cover the board without impacting it's acoustical
properties. These are 4" thick 2ft x 4ft boards and I will probably
take them to a local shop to have the material sewn around the board,
kinda like "slipcovers" for living room furniture. But while I'm
still waiting for the board to be delivered, I want to confirm that
there is nothing better than raw burlap for this purpose? Although
the most important purpose of these boards will be to control bass
frequencies, I would prefer that the cloth covering not impact the
acoustical properties of the board at any frequency (if possible). Is
there anything other than burlap that I should be considering?

Thanks.

Steve