Abstract: The invention proposes a lightweight vertically perforated brick having a perforation pattern comprising perforations which form a plurality of perforation rows, extending in the longitudinal direction, and are separated from one another by webs. In order to achieve an improved coefficient of thermal conductivity and to reduce the flank transmission, the invention proposes the combination of the following features: thickness of the webs .ltoreq.5 mm, ratio of the largest and smallest inside widths of the perforation cross-section is between 1:1 and 1:2.5, spacing of the perforation rows .ltoreq.22 mm, proportion of perforations .gtoreq.50% and apparent density of the brick material .gtoreq.1.5 kg/dm.sup.3. Hexagonal perforations, with corners directed towards the side walls, and a fibrous porosity agent are to be preferred.