The mechanical properties and water resistance of thermo-moulded films made from a sunflower protein isolate plasticized with glycerol (ratio 2:1, w/w) were studied. Various cross-linked or hydrophobic components (aldehydes, plant tannins, alcohols and fatty acids) were added and the properties of the films obtained with those of control films (containing no additives other than the plasticizer) were compared. The use of octanoic acid resulted in high tensile strength (7 MPa), whereas the use of octanol resulted in great increase in tensile elongation (54%). Plant tannins gave films with properties similar to those obtained with aldehydes, but without the toxicity. The network of proteins formed by thermo-moulding is water-resistant, regardless of which additives were used or their nature.