We're in the midst of a renovation on our 1959 brick rambler and have discovered that the original masonry walls had NO insulation whatsoever. (This certainly accounts for much of our frustration with heating and cooling the place.)

I'd like to insulate every exterior, uninsulated wall, but to sacrifice as little interior floor space as possible.

From some very superficial research, I've found a company called Plymouth Foam has some interesting options:

http://www.buildwithplymouth.com/products/goldwall.html

The one I found here is essentially a self-furring insulation product. Because it's self-furring, it saves our crew the effort of installing furring strips and/or creating traditional insulation cavities with 2 x 4 or 2 x 6 framing. It also comes in a variety of thicknesses, and I assume one of the advantages of this product is that it might save some floor space.

Another option, apparently, is to use steel furring channels... and I'm sure there are a million more options. Honestly, it's hard for me to evaluate what the best insulation (in the thinnest possible package) might be.

Do any of you have experience with this (or other) products that might solve our problem?