The purpose of this standard is to establish the classification, designation and specifications of expanded polystyrene (EPS) lightening parts used in concrete floors with ribs poured in situ, both unidirectional and reticular (bidirectional). This standard is applicable to all types of expanded polystyrene parts obtained by machining blocks or by molding said material, with lightening functions. For expanded polystyrene pieces used as lightening in floors made with prefabricated joists, EN 15037-4 is applicable.