the fibers in cold face layer 6 in that they will be significantly more temperature resistant among the various fiber combinations which can be used include a hot face layer 4 composed of alumina fibers 3000 u00b0 f 1670 u00b0 c service temperature and a cold face layer 6 composed of silica alumina chromia fibers 2600 u00b0 f 1430 u00b0 c service temperature a hot face layer 4 composed of the aforementioned silica alumina chromia fibers and a cold face layer 6 composed of conventional aluminosilicate fibers 2300 u00b0 f 1260 u00b0 c service temperature a hot face layer 4 composed of the aforementioned aluminosilicate fibers and a cold face layer 6 composed of any of the fibers described in u s pat no 4 055 434 to a b chen and j m pallo 1400 u00b0 f 2000 u00b0 f 760 u00b0 c 1090 u00b0 c service temperature or a hot face layer 4 composed of the aforementioned fibers of u s pat no 4 055 434 and a cold face layer 6 composed of any conventional glass fiber mineral wool fiber or rock wool fiber other combinations such as the silica alumina chromia fibers in the hot face layer 4 backed up by the fibers of u s pat no 4 055 434 in the cold face layer.