The invention relates to a method for producing tear-propagation-resistant foils using biologically degradable polyesters which can be obtained by polycondensation from: i) 65 to 80 mol %, based on components i to ii, of one or a plurality of dicarbonic acid derivatives or dicarbonic acids selected from the group consisting of: succinic acid, adipic acid, sebacic acid, azelaic acid and brassylic acid; ii) 35 to 20 mol %, based on components i to ii, of a terephthalic acid derivative; iii) 98 to 102 mol %, based on components i to ii, of a C2-C8 alkylene diol or C2-C6 oxyalkylene diol; iv) 0.05 to 2 wt %, based on the polymer obtainable from components i to iii, of an at least trifunctional crosslinker or of an at least difunctional chain extender. The invention further relates to polymer mixtures which are suitable for producing foils capable of tear propagation.