Hi there...

I despise the itchy kind of fiberglas, I got into enough of it building my house not to want to get into it again. It's potentially highly toxic too, and decays in a way where burlap will definitely not hold in the smallest particles, which are the most toxic.

Now I have used something called "mineral wool", which is just not itchy the same way. We used this in building a masonry stove, where it got too hot for fiberglas. This stuff seems downright wholesome, and to quote from the Acoustics FAQ, which I'm working through,

"When assessing rigid fiberglass, it is important to know its density so you can compare equivalent products. Owens-Corning 703 has a density of about three pounds per cubic foot (45 kilograms per cubic meter), and 705 is about six pounds per cubic foot (90 kilograms per cubic meter). Therefore, products from other companies that have a similar density will have similar absorption characteristics at the same frequencies. Note that some companies call their products mineral wool, mineral fiber, or rockwool, but acoustically they are equivalent to fiberglass."

So, apparently I can get the desired results without the itchiness and particulate hazard of fiberglas? This interests me a lot, and would get me moving putting the stuff up in the house/studio.

Just trying to clarify and confirm this, and to see if there's some confusion about what all is called "mineral wool". Also have encountered "rock wool" which seemed benign enough.

Ted,

I'm not aware that rigid fiberglass "decays." And as far as I know rigid fiberglass, rigid mineral wool, and rigid rock wool are all pretty much the same thing. I've used only rigid fiberglass, but my understanding is the others are merely made from a different type of "rock."

But if you're concerned about particles leaking into the air you can always cover it with a denser fabric. Many people think you need fabric that's acoustically transparent. But that's not so. As long as the material is not shiny and reflective it will work fine for covering absorber panels. For example, felt is thick and dense enough to keep all particles in place. If it absorbs a tiny bit more on its own, no harm is done.

--Ethan

From what I've heard about the decay, it's a matter of decades.

Felt is just too excellent and obvious of a solution for me to have thought of it! Thanks!