Thanks Nowak and groundcontrol
Mark - the product you refer to is called rigid fibreglass.
KNAUF and
OWENS CORNING both make it.
Normal pink batts put on a wall will absorb down to around 800hz and rolls off quickly after that. This rigid fibreglass will absorb down to 500hz and tapers off
slowly and is still working at 250hz and 125hz.
This is still creating an inbalance in the room as the low-mids and lows are still active in the room. Some form of low frequency absorption in the room is required in the form of bass traps and slot resonators.
cheers
John