The general consensus is that foam is of relatively little use when it comes to the low end. I'm of the opinion that it's fairly limited in its usefulness overall in fact, and that most situations would probably be far better tackled by some mineral wool panels/traps.
I'm sure someone has done some tests, but I've never gone out of my way to find any based on my above opinions!
All the commercial foam 'bass traps' I've seen are far too small to be effective in the bottom couple of octaves. I share Sam's view that larger traps built using mineral wool, possibly with a limp-mass membrane, are far more effective, and usually cheaper, too.
Technical Editor, Sound On Sound...
(But generally posting my own personal views and not necessarily those of SOS, the company or the magazine!)
In my world, things get less strange when I read the manual...
There are reasons why foam is looked down on. For a start there is usually only half of it there! Due to the pyramid cutting. But foam designed for purpose, e.g. RPG and Auralex, Melamine, absorb pretty much exactly the same as equivalent fibre. The original StudioTips SuperChunk was tested alongside the same sized MegaLenrd, identical performance. Actually the foam slightly better than the Fibreglass. However note as Hugh has, small corner traps be they Lenrds or the 60cm wide version of the SSC, are really very disappointing. Go big or go home....