Jim,
The problem with foam is that the effective range rolls off way too soon. So what happens when you use foams? You kill the highs and mid-highs and mids, while leaving low mids and lows untreated. Where are the problem areas, acoustically, in most small and home studios? In the low mids and lows.
Foams can be used to augment and assist a well-trapped room, but usually you can get better performance over a wider audio bandwidth by using some rockwool or solidified fiberglas product... we typically talk about OC 703 or 705 as a shortcut, but really all the major insulation manufacturers make similar products, not just Owens Corning.... wrapped in an attractive cloth or architectural fabric.
My last studio was lined in bass traps based upon Ethan Winer's designs, and I used various thicknesses of 703 to control flutter echoes between parallel surfaces, wrapped in unbleached muslin, glued into small wooden trays, and mounted from the ceilings and walls at various angles. My home writing room was tricked out in a Real Traps room kit.
You can get boatloads of information from Ethan's personal site, and from his company website. (ethanwiner.com and realtraps.com)
Bill