Abstract: A new curable urethane composition which comprises a polyhydroxyl component and a polyisocyanate component, wherein said polyhydroxyl component comprises80 to 10% by weight of an interesterification product (A) which is the reaction product of castor oil (a1) and substantially non-hydroxyl-containing naturally occurring triglyceride oil (a2) and, optionally, low molecular weight polyol (a3) and20 to 90% by weight of a polybutadiene based polyol (B).The composition has a sufficiently low viscosity to be easily handled and forms a polyurethane resin with excellent elongation and electrical properties.