Starch directly functionalised in the plant by modulation of its biosynthesis by mutagenesis and transgene technology was exploited for its extended functionality beyond the normal variation. In this study we investigated the rheological and mechanical properties of films from such structurally highly different starch types derived from potato and cereal sources of normal and mutant and transgenic backgrounds. A new improved technique was developed to permit the dynamic mechanical analysis of films in the presence of water. It was found that the amylose content was decisive for the mechanical properties of the films – an increase in the amylose content resulted in both a higher stress and strain at break. Interestingly, there was no correlation between the speed of hydration and mechanical water resistance of the films. Generally, the films were clear and transparent, even after wetting. Transgenic potato starch with a low content of phosphate displayed an extraordinary combination of high robustness, transparency, mechanical strength and extensibility even in a wet condition. The combination of optimal phosphate and amylose concentrations in this sample probably favoured hydration and amorphisation without compromising the inter-chain interactions of the polysaccharide network.