EPS—ExpandedPolystyrene

Sintered Expanded Polystyrene (EPS) has democratised energy efficiency. It is the backbone of building renovation (Superbonus), enabling the entire building to be wrapped in a continuous thermal layer that eliminates thermal bridges at a fraction of the cost of other insulators.

Via high-temperature steam injection and a blowing agent (pentane), polystyrene beads expand up to 50 times their original volume. In a closed mould, a second steam burst permanently fuses the bead edges (sintering), creating a block of a billion microscopic closed cells. These cells trap air, stopping convective movement: EPS becomes a masterful insulator while being 98% air and only 2% actual plastic material.

Unlike totally closed-cell polyurethanes, standard white EPS maintains reasonable vapour permeability (mu 30 to 70), similar to dense wood. Its main limitation is UV sensitivity (left raw in sunlight it yellows and crumbles to dust in months) and instant dissolution in contact with chemical solvents.