Okay, after playing with 1.23 on SSP, construction foam is similar to obsidian, even in that it blocks nukes semi-well. It's also paintable, and 1clay block+1coal+1redstone+1water cell(1/4tin)=3 foam-(compressed)> 3 CF pellets=6 sprays of the CF sprayer it seems, and that's 13foam per spray if it can put it all out. Just some data for those of you crunching numbers and trying to decide what is more cost-effective.
In order to run 1.23, you have to update your MCForge to 1.1.2 or it will not run.
Oh, and when painting the hardened foam I heard Tetris music in the background. This stuff is pushable with pistons by the way, so those of you who want to be more efficient can instead of trimming off badly placed foam can instead use a piston to push it around.