comprised of warp fibers 55 and fill fibers 50 in a preferred embodiment of the invention the compressible sealant comprises polyurethanes formed by the reaction of a diisocyanate and a polyol preferred diisocyanates can include toluene diisocyanate methylene bisphenyl isocyanate hexamethylene diisocyanate and isophorone diisocyante the resultant polyurethane is self curing and requires no vulcanization the polyurethane must have a viscosity of about 0 5 to 200 centipoise prior to curing to be able to flow into the narrow gap and form the compressible sealant the microspheres are incorporated into this polyurethane based compressible sealant prior to the curing process the resulting hardness of the cured compressible sealant of the present invention is in the range of about 50 shore a to about 90 shore a and more preferably in the range of about 60 shore a to about 75 shore a such levels are relatively soft compared to most polymers the compressible sealant of the present invention has several advantages over the prior art one is its excellent compression set this parameter is measured by compressing a polymer to 75 of its original volume and holding the polymer in this compressed state at 70 degrees c for 72 hours the pressure is then released from the polymer and the recovery volume.