The invention relates unsaturated polyester resins for the manufacture of subzero flexible, weather-resistant products. The liquid unsaturated polyester resin comprises a linear unsaturated polyester obtained by reacting 5-30 mol % of one or more ethylenically unsaturated dicarboxylic acids (A), 20-45 mol % of one or more other aliphatic or aromatic acids (B) and 40-60 mol % of two or more polyhydric alcohols and 30-60 wt % of one or more reactive monomers. The linear unsaturated polyesters have a cone and plate viscosity (I.C.I.) of 2 ps/125° C.-20 ps/125° C. and a molecular weight Mw of 20,000-100,000. The invention also relates to a process for the manufacture of such unsaturated polyester resins and to the use of them in applications wherein good adhesion to supporting material and flexibility at ambient and especially at low temperatures are needed.