BuildBlock ICFs are pre-assembled blocks composed of expanded polystyrene (EPS) foam and connected by high-density plastic webs. The foam blocks are stacked together to form hollow walls in which steel rebar is placed, and concrete is poured. ICF walls are essentially steel-reinforced, solid concrete wall that’s insulated on both sides. BuildBlock ICFs build incredibly strong and energy-efficient walls that outperform traditional wood-frame walls.