An additive elastomeric manufactured part having improved surface finish is made by repeatedly extruding through a nozzle to build up layers of a material comprised of a prepolymer comprised of an isocyanate terminated prepolymer and a filler in an amount such that the material has a shear storage modulus G′ of 100,000 to 300,000 Pa measured at an oscillation rate of 1 Hz and a relaxation time of 20 seconds to 360 seconds. It has been discovered that the particular material having these rheological properties is able to improve the surface finish of the additive manufactured part without slumping and is believed to be due to surface flow of material into valleys between the extrudates as they are being built up.