The invention is a composition comprising a) one or more isocyanate functional polyether based prepolymers containing one or more organic based polymers dispersed therein; b) one or more isocyanate functional polyester based prepolymers which is solid at 23.degree. C.; c) one or more polyisocyanates having a nominal functionality of about 3 or greater; d) one or more conductive carbon blacks in an amount such that the composition has a dielectric constant of about 15 or less; and e) one or more catalysts for the reaction of isocyanate moieties with hydroxyl groups, wherein the composition demonstrates upon cure a modulus of 2.0 MPa or greater at 25.degree. C. measured according to ASTM D4065; a dielectric constant of about 15 or less; a sag of an uncured sample of less than 2 mm, a press flow viscosity of about 20 to about 50 and a storage modulus of about 5.3.times.10.sup.5 Pa or greater.