The synthesis of linear and crosslinked polyurethanes based on α,ω-dihydroxypolydiethylene glycol terephthalate (PDET) is described. Prior to the preparation of these materials, a PDET polymer was obtained by conventional condensation reaction between dimethyl terephthalate and diethylene glycol, and a well-characterized fraction of PDET with number average molecular weight of 3,650 g mol−1 was chosen for the synthesis of the polyurethanes. Specifically, three polyurethanes were prepared: a pure linear polyurethane by reaction of PDET with 4,4′-diphenylmethane diisocyanate (MDI), a chain extended polyurethane obtained with MDI, PDET and 1,4-butanediol as chain extender, and a crosslinked polyurethane synthesized from PDET and a polyfunctional isocyanate. Thermal, mechanical, dielectric and gas transport properties of the polyurethanes were studied, showing excellent performance. In particular, rubber-like flexible materials were obtained with elongation values over 1000%, due to the low glass transition temperature of PDET. Furthermore, it was observed that these materials, in particular the crosslinked polyurethane, behave as gas barriers.