Varnishing of the printed product is often carried out by means of a photopolymer flexographic printing plate. Various types of varnishes interacting with a photopolymer material can cause chemical changes in its surface layer and affect the acceptance and transfer of varnish to the print. The aim of this paper is to describe the interactions of different types of varnishes and standard styrene-isoprene-styrene flexographic printing plate and to analyse the influence of varnishes on the surface layer of the photopolymer material. Types of varnishes used in this research are matt and gloss water-dispersive varnish, oil-based and UV varnish. Their interactions with the printing plate were analysed using different methods: contact angles of the varnishes on the printing plate were measured, and surface free energy of the printing plate was calculated before and after application of the varnishes. Experiments of the swelling of printing plate were carried out in order to assess the effect of the varnishes on the chemical changes in the photopolymer material. Microscopic images of the photopolymer exposed to varnishes and FTIR-ATR spectra were obtained in order to capture visible changes on the printing plate’s surface. The results of the research will allow for an assessment of the suitability of a specific type of varnish for flexographic printing.