Alternative absorbent acoustic material?

I finally read the owner’s manual that came with a pair of speakers I bought last spring (Revel M126Be) and there is a a couple of paragraphs that talk about treatment materials. Revel states that: "There are numerous options for absorbent material. None are superior to low-cost fiberglass." And it goes on to say that "It is important to use absorbers that are at least 4 inches thick, to avoid altering the spectral response of the loudspeakers." It also says that "Sculpted foam is less efficient" and needs to be "at least 8 inches thick."

I assume that the low cost fiberglass that Revel is referring to is the insulation that comes on a roll that is available from, for example, Lowes? Has anyone tried this, and if so how did it work out?