Thin boron nitride films were deposited using ion beam assisted deposition. The fraction of the cubic phase relative to the non-cubic phase was varied by changing the assisting ion to boron atom arrival ratio during deposition. Different ex situ analytical techniques were used to resolve the layered growth, i.e. cubic BN on top of non-cubic BN. Variation of the argon incorporation measured with Rutherford backscattering spectroscopy yields information on the layered growth. Polarized IR reflection data were analysed with a multilayer model taking into account the anisotropy of hexagonal BN. The parameters of the optical model, such as the thickness of the non-cubic BN interlayer and the volume fraction of cubic BN in the toplayer, are more useful for the characterization of BN films than the established IR peak ratio. Reflection electron energy loss spectroscopy and X-ray reflectivity measurements were also performed to verify the results.