If you have a silk touch pickaxe (or another tool), you can harvest Construction Foam blocks (unhardened ones).
Then compress it for CF pellet, spray, and reharvest for more Construction Foam.
Simply way to get "infinite" construction foam, at least until your Silk touch tool runs out of uses =P
Tested SSP/SMP MC 1.25 IC² 1.95
Construction Foam > Compress > Spray > Harvest 13 Construction Foam Blocks >
Profit?
Construction Foam cannot be harvested on intention.