Basotect(click)....way more efficient than any of the ATS and GIK materials....and waaay more cheaper. It’s used in trains, plains, industry and probably (90% chance) in your car’s headliner.
And ehm rockwool, mineral wool and other fiberglass insulation materials are soo 1980....I thought we’ve already evolved from the olden days. 
I’ve used about two cubic meter to treat my living room.
Super easy to use, and, more important...no need to change your shirt !! 
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?