We describe the formation process of thin films consisting of surface-attached polymer networks formed through C, H-insertion based cross-linking (CHic process). To this thin films of polymers containing benzophenone or sulfonyl azide groups are photochemically or thermally activated, which leads to simultaneous cross-linking and surface attachment of the deposited polymer. A simple percolation model is used to describe the formation of such polymer networks as a function of reaction time and reaction conditions. It is based on known parameters such as the kinetics of the activation of the cross-linker, cross-linker contents, molecular weight of the polymer, film thickness, temperature (respectively the light dose), and absorption coefficient of the polymer. The developed model allows, with only one adaptable parameter, namely the efficiency factor j, the prediction of the complete cross-linking behavior of CHic reactions. The kinetic model enables the identification of suitable conditions for network formation and thus facilitates to use this very simple and versatile method to generate tailor-made surfaces.