Abstract: A flexible, adjustable refractory filler (1) is disclosed for filling gaps between ceramic tiles (10, 11) forming the heat shield of a space shuttle vehicle, to protect its aluminum skin (20) during atmospheric re-entry. The easily installed and replaced filler (1) consists essentially of a strip of ceramic cloth (3) coated, at least along both its longitudinal edges (4, 5), with a room temperature vulcanizable silicone rubber compound with a high emittance colored pigment. The filler may have one or more layers (2, 3), as the gap width requires. Preferred materials are basket-weave aluminoborosilicate cloth, and a rubber compounded with silicon tetraboride as the emittance agent and finely divided borosilicate glass containing about 7.5% B.sub.2 O.sub.3 as high temperature binder. The filler cloth strip or tape is cut to proper width and length, inserted into the gap, and fastened with previously applied drops of silicone rubber adhesive.

Abstract: Polyimide foam products having greatly improved burn-through and flame-spread resistance are prepared by the reaction of aromatic polyisocyanates with aromatic dianhydrides in the presence of metallic salts of octoic acid. The salts, for example stannous octoate, ferric octoate and aluminum octoate, favor the formation of imide linkages at the expense of other possible reactions.