Abstract: A process for manufacturing a heat insulating material including alumina based fibers and aluminosilicate binder. The process includes the steps of: (a) milling alumina based fibers, having a mean diameter less than or equal to 2 .mu.m, in water until a mean aspect ratio (l/d) of 30 to 130 is obtained; (b) vacuum molding a billet from the resulting aqueous, fibrous, flowing slurry; (c) fixing the billet in a frame, while compressing it slightly; (d) drying the slightly compressed billet in the frame to form a dried billet; (e) preparing an aluminosilicate binder having low durability; (f) impregnating the dried billet, fixed in the frame, with the binder; (g) gelling the binder to produce a semi-finished product; (h) removing the semi-finished product from the frame; (i) drying the semi-finished product; and (j) firing the semi-finished product.