the present invention relates to water - resistant , thermoplastic starch materials processable into environmentally safe , thermoplastically produced products and cast sheets , which consist of starch acyl compounds , obtainable from high amylose starches and the derivatives thereof and being sparingly soluble in water , and of plasticizers which like ethyl citrate , glycerol acetate and lactic acid ester have a gelatinizing effect and preferably a dissolution property resulting in brilliant transparence and , as can be proved , are biodegradable .