The selection of the isocyanate prepolymer will influence most of the properties of the polymer. The % of NCO will influence hardness, stiffness, strength properties, speed of reactivity. The “backbone” will influence the type of chemical/solvent resistance, as well as strength properties. The functionality (number of reactive sites per molecule) of the prepolymer will affect the temperature resistance, hardness, stiffness, impact resistance and elongation. The isocyanate can be aliphatic or aromatic. This selection will affect the UV stability, as well as other physical properties. The formulator may add other chemicals to the prepolymer, especially a diluent to lower the viscosity, and slow down the reactivity of the system. The viscosity of the system will greatly affect the processing of the polyurea.