EPS (expanded polystyrene) Type II: R-4.0 per inch. ASTM C578. Density: 1.35 lb/cf. Compressive strength: 15 psi. Uses: below-grade foundation walls, under slab (non-structural), exterior continuous insulation (CI), EIFS substrate, ICF cores. Advantages: lowest cost rigid insulation, does not absorb significant moisture (closed-cell), stable R-value over time (no thermal drift like XPS), recyclable. Moisture absorption: 2-5% by volume over 30 years. Under-slab: place below vapor barrier on compacted fill. CI walls: adhesive + mechanical fasteners, taped joints. Fire: ASTM E84 Class A (with thermal barrier per IBC 2603). Must be protected from UV. Thickness: 1, 1.5, 2, 3, 4 in sheets (4x8ft). Cost: $0.25-$0.50/sf per inch. CSI 07 21 13.