Acoustic Properties of Compressed Loft Insulation Rolls

I am moving house shortly and at the planning stage for my new studio. I am going to use rock wool loft insulation rolls stacked in the corners for bass trapping. However I have noticed that most of the DIY sheds now only seem to stock loft insulation in compressed form that expands when you open the pack. So my question is - will these have the same effect on the bass when they are still in compressed form or will I have to open them up, unroll to expand and then try to roll them back up again?

http://www.wickes.co.uk/loft-roll-insulation/invt/161210/

Unfortunately the more you compress it, the less well it works as a bass trap. This is because it's smaller, for a start - it doesn't interact with as much of the cycle at longer wavelengths. And it's a double whammy, because you are also tempted to put the rolls further into the corners - another mistake. In the corners, there's a velocity to pressure conversion, and the trap only works on the velocity. The idea is that you have to slow down the wavefront over a significant portion (at least 1/4 of a wavelength), and it has to pass through the material in order to be slowed and converted to heat. Compression gets in the way of this in just about every way you can think of!

Thanks Steve. Suspected that something like that might be the case. 

The optimal density for bass trapping would be Rockwool RW3 products also know as Rocksilk.

I made my own bass traps from this product and they are superb, always ensure you wear protective
goggles, a long sleeve shirt and a dust mask when handling such products, then they are quite safe.

SafeandSound Mastering
music mastering

I have a couple bundles of still in the package fiberglass batt insulation stacked up in the corners of my little mix room, behind my monitor stands.  Covered them with a light curtain for aesthetic reasons.  They definitely helped the bottom end.  Whether they helped as much as a properly built up bass trap is a larger question.  I usually go to the acoustics/studio construction forum at recording.org or the John L. Sayers forum for this sort of thing.  Lots of info and clever folks to be found.