Porotherm is a terracotta block engineered by Wienerberger AG for both structural and thermal use. The exterior wall of Haus 2226 by Baumschlager Eberle Architekten has two vertical layers, or wythes, of Porotherm, totaling 760mm (30 inches). The outer wythe has more openings or voids inside to trap air and resist heat flow, so no other insulation is required. The inner wythe has more solid material, making it strong enough to provide the vertical structure, and to store heat as thermal mass. The special mortar bonding the blocks together is a thermal bridge, because it conducts heat more readily than the surrounding blocks. To minimize the heat loss, the horizontal mortar joints of the outer and inner wythes do not align and there is no vertical mortar between the wythes. These drawings use color to show the temperature inside the walls if we could cut through them.