A biodegradable polymer includes a) 20 to 60% of a mixture of starch and/or a modified starch, b) 8 to 22% of starch plasticisers and processing agents c) 30 to 70% of one or more biodegradable aliphatic polyesters d) 1 to 10% of a layered silicate clay mineral. The silicate mineral is an organoclay which has been formed by reacting clay with an intercalating chemical to compatibilise it with the polymers so that the clay is exfoliated and makes the blend amorphous. The polymers may also include the usual additives including e) from 0 to 20% by weight of a polyol plasticiser f) from 0.1 to 1.5% by weight of a C.sub.12 22 fatty acid or salt or a destructing agent preferably urea and/or urea derivatives, and g) from 0 to 12% by weight of added water. The polyester may be modified by reaction with maleic anhydride.