Finite element method (FEM) modeling of the island blister test (IBT), which takes into account the possibility of plasticity in the film and can separate the normal and shear components of the specific fracture energy, is presented. IBT specimens of a polymer film (Ultradel 4212) on a chromium-coated silicon substrate were prepared and tested using modified procedures which am described. The analysis of the experimental results shows that crack propagation occurs when the mode I component of the specific fracture energy reaches a critical value.