Prismatic liquid hydrogen tank

A prismatic tank for the containment of a liquefied gas, the tank comprising a plurality of substantially planar side walls defining two opposing ends, two opposing sides and an upper surface opposing a lower surface, the planar side walls defining a volume for containing a liquefied gas, the prismatic tank further comprising edge portions at the intersection of the planar side walls and an outer insulation layer arranged on the outer surfaces of the substantially planar surfaces and on the outer surfaces of the edge portions, wherein the edge portions and the planar side walls are extrusions, and wherein the insulation layer is in the form of a modular insulation arrangement comprising one or more tessellating insulation units, each unit comprising a first inwardly facing layer and a second outwardly facing layer spaced from the first layer, the two layers defining a space there between and one or more spacing members extending between the first and second layers, and wherein the surfaces defining the first layer, the second layer and the outer perimeter extending around the arrangement are air impermeable surfaces.