The system I use to build, Nudura, is a foam form that you build on site. We run horizontal and vertical steel (reinforcing bar) through it and pour concrete into the 6″ cavity. This leaves you with a building that has the structural strength of reinforced mass concrete, but with the excellent insulation inside and out of the foam (u-value 0.11). When you take into consideration Nudura ceiling insulation, and careful attention to air tightness, your home will be built to the highest possible “A” energy rating.
For further technical explanation, please visit Nudura’s own website.