The linear dependence of the wavelength of the instability on the film thickness is similar to previous observation where a negative hydrostatic stress develops in the film. However, the proportionality constant between wavelength and thickness is found to be lower than that observed previously. A detailed theoretical analysis is required in order to unravel the reasons for this difference although from the outset, we note that the microscopic elastic property of the H-PDMS film is heterogeneous which differs from the previous studies. Furthermore, as the matrix swells, its elastic property is expected to change rather non-linearly in these highly deformable systems, which would also have to be considered in the detailed analysis of the problem.