High-performance polystyrene foam thermal insulation with a 1-cm concrete crust made with special adhesives for the thermal insulation of inverted flat roofs and attic walls. The thermal insulation material is manufactured by an extrusion production procedure, the result of which is a homogeneous material structure, a smooth surface crust (called extrusion crust) and a number of favourable material characteristics. The concrete crust on the upper side of the thermal insulation boards provides long-term UV protection and a walkable surface due to its excellent mechanical resistance. Due to its low mass/m2 and high strength, the ROOFMATE LG is suitable for the quick and efficient insulation of flat roofs which cannot be loaded with a heavy gravel layer. It is also suitable for the thermal insulation of the inner side of attic walls of flat roofs.