Sorry, I find the acoustical treatments master thread unwieldy and of limited use for specific questions sometimes.

So if I were to make bass traps out of Roxul RHT 40 instead of OC703, here's some thoughts:

Roxul RHT 40 comes in 3" thick 3.5 pcf (.62 @ 125 hz)

OC703 comes in 2" thick 3.0 pcf (.53@ 125 hz)

While the absorption isn't exactly the same according to bobgolds.com it is pretty close.

So for corner bass traps, it would appear to be easier to cut (with fewer cuts to make a stack), similar absorption, and is about half the cost. I will still be using OC703 for the rest of the treatments.

Is there any downside?

Has anybody else used this stuff?

A quick conversation with Bryan Pape set me straight. I'm back on the OC703 bandwagon. (Well, actually OFI-48....but that's a while other story).

why are you back on the 703 bandwagon, i used rockboard 60 for my traps, have you heard of a disadvatage to roxul?

A lot of it came down to my own application. Some of the 2" OC703 that Bryan specced for me will not be used in the bass traps, but in other treatments.

He did mention that it crumbles a bit more than OC and is actually harder to work with.

To be honest, I was just looking to cut costs, so the difference probably doesn't make it worth it for me to source multiple types.