Quote: Originally Posted by ashebiara Mr. Ethan , in the case of the limp mass aproach, could it work even with none rigid fiberglass?? or does it have to be a rigid fiber glass for the cling wrap to work as it has to in this type of assembly?? i am making basstraps with , mineral wool of 4"thick 2'x4', but the mineral wool that i got it's not fluffy like de R type insulation nor it is rigid like de 703 wich in fact looks very rigid to me.. anyways i just plan to glue the plastic directly to de mineral wool insulation and then put it on the frame and make the whole asembly with the fabric ( burlap in the front/muslin on the back) ... Yes the membrane will work with the mineral wool. It is done that way on mineral wool all the time.