A vegetable oil-based polyol is made by adding a peroxyacid to vegetable oil wherein said peroxyacid reacts with said vegetable oil to form epoxidized vegetable oil and adding said epoxidized vegetable oil to a mixture of an alcohol, water, and a catalytic amount of fluoboric acid so as to form a vegetable oil-based polyol. A further embodiment of the present invention involves making a vegetable oil-based polyol using an epoxidized vegetable oil as the starting material. The epoxidized vegetable oil undergoes hydroxylation by the same process as outlined above. According to another aspect of the present invention, the vegetable oil-based polyol formed by the novel methods of this invention may be reacted with an isocyanate to form a polyurethane. Alternatively, a filler such as silica may be combined with the vegetable oil-based polyol before it is reacted with the isocyanate. These polyurethanes made from vegetable oil-based polyols may be used to form electroinsulating casting resins.