A heat exchanger including a casing including aluminum nitride impregnated alumina-silica cloth. The heat exchanger includes a hot fluid flowpath positioned inside the casing for carrying a hot fluid from an inlet to an outlet downstream from the inlet. The hot fluid flowpath is formed at least in part by a thermally conductive wall permitting thermal energy to transfer from hot fluid flowing through the hot fluid flowpath. The heat exchanger includes a cold fluid flowpath for carrying a cold fluid from an inlet to an outlet downstream from the inlet. At least a downstream portion of the cold fluid flowpath is formed by the thermally conductive wall permitting thermal energy to transfer from hot fluid flowing through the hot fluid flowpath to the cold fluid. At least a portion of the cold fluid flowpath upstream from the thermally conductive wall is formed by ceramic foam.