The degree of liquidity developed in each case depends principally on the proportion of solvent to asphalt cement. To a minor degree, the liquidity of the Cutback Bitumen may be affected by the hardness of the base asphalt from which the cutback is made. The degree of fluidity results in several Grades of Cutback asphalt—some quite fluid at ordinary temperatures and others somewhat more viscous. The more viscous grades may require a small amount of heating to make them fluid enough for construction operations.