Abstract: Biodegradable polyether esters P1 obtainable by reacting a mixture essentially comprising (a1) a mixture essentially comprising 20-95 mol % of adipic acid or ester-forming derivatives thereof or mixtures thereof, 5-80 mol % of terephthalic acid or ester-forming derivatives thereof or mixtures thereof, and 0-5 mol % of a compound containing sulfonate groups, where the total of the individual mole percentages is 100 mol %, and (a2) a mixture of dihydroxy compounds essentially comprising (a21) from 15 to 99.8 mol % of a dihydroxy compound selected from the group consisting of C2-C6-alkanediols and C5-C10-cycloalkanediols, (a22) from 85 to 0.2 mol % of a dihydroxy compound containing ether functionalities of the formula I HO—[(CH2)n—O]m—H  I where n is 2, 3 or 4 and m is an integer from 2 to 250, or mixtures thereof, where the molar ratio of (a1) to (a2) is chosen in the range from 0.4:1 to 1.