" A promising sort of material would be one that absorbed sound (rather than re-directing the air flow as leather does). Traditional sound absorbers are fabrics, such as batting, or knotted carpets. More recently, a number of high-tech sound absorbing fabrics have been devised which may work somewhat better, and are quite a lot thinner--very important in the restricted space of a concertina end.

Sound-absorbing acoustic fabric
produces a different sound quality The material I tried is a rough ribbed polyester fabric made by JM Lynne Co. and sold on the net by Netwell Noise Control under the name "silence wallcovering" for application to the walls of rooms; it is said to be "designed for light sound absorption where the human voice and other mid range sound sources are a culprit". It is thin: 0.175" (about 4.4mm). The mill width is 54 inches, so a single linear yard at that width will cut out into a dozen or more pairs of baffles, even large ones; it is light in weight, with a linear yard (54" wide x 36") weighing 24 ounces. The fabric is available in 24 colors ( I have used black and ivory.) A yard costs USD 22.50 (GBP 15.85, EUR 25.60). See below under Suppliers.

This particular acoustical fabric is not at all air-tight--if you hold it to your lips you can blow through it just about as easily as through a single layer of ordinary t-shirt fabric. "
in www.concertina.com
(http://www.concertina.com/gaskins/baffles/)

• Acoustical Fabric