This master’s thesis is focused on the study of chemical and physical properties of dielectric materials with main focus on epoxy resins. It includes possible processes that can influence the properties of epoxy resins, both processes that improve polymer properties and processes that cause material degradation. Next part of the thesis is a description of diagnostic methods suitable for measurement of basic electrical quantities of material and design of a suitable method for measuring properties of epoxy resins with different additives, influencing the samples by solar radiation. At the end, the work includes an experiment dedicated to the degradation of epoxy resins with various additives by solar radiation and the evaluation of the experiment.