A process for the preparation of an unsaturated polyester from a glycol and tetrahydrophthalic anhydride, maleic anhydride and/or fumaric acid, suitable for the production of an unsaturated polyester resin rapidly loosing its surface tackiness after cross-linking, and furnishing very flexible materials which are resistant to creasing, is described. The glycol employed has at least two ether bridges regularly alternated with --CH.sub.2 --CH.sub.2 -- groups. The reaction is carried out in such a way as to obtain an alkyd essentially exempt from free tetrahydrophthalic anhydride. The resins thus prepared are adapted to the production of putties free from surface tackiness and having good finishing properties for application by spraying and/or by putty knife.