Thermally insulating wall structure particularly for kilns

A wall structure for thermally insulating an enclosed space to be heated such as a ceramic kiln, said enclosed space being defined by four side panels and top and bottom panels, said wall structure comprising a a layer of an air-permeable thermally insulating material located adjacent to and coextensive with, but spaced from the exterior surface of at least one of said panels, to define an internal chamber, and an external chamber formed by a panel located adjacent to and coextensive with said insulating material on the opposite side of said insulating material from said internal chamber, means to enclose said internal and external chambers such that air flow therethrough is restricted to passage through said insulating material, said external chamber having at least one air intake mouth and said internal chamber having at least one air exhaust mouth leading to said enclosed space, air supplying means effective to create an air flow from said intake mouth to said exhaust mouth, whereby said air passes from said external chamber, through said air-permeable thermally insulating material wherein said air is heated and thereafter passes into said internal chamber and into said enclosed space.