Did you know? Some have horizontal perforations (hollow bricks), while others have vertical perforations. Those with horizontal perforations must conform to the specifications laid down in French standard NF P 13-301; for vertically perforated bricks, the standard is XP P 13-305. The "NF" (Norme Française) quality label identifies products which have been certified in conformity with French national standards. Their use is regulated by French standard NF P 10-202 "small masonry unit walls" and subdivisions: référence NF P 10-202-1 : "Technical specifications" référence NF P 10-202-2 : "Calculation rules and minimum construction provisions" référence NF P 10-202-3 : "Guideline to choose the type of façade walls according to the site".