To highlight the main factors involved in the degradation of polymers in multilayer films under γ-irradiation, the ANOVA Common Dimensions (AComDim, Analysis of Variance in Common Dimensions) method is applied on spectra recorded with ATR-FTIR (Attenuated Total Reflection-Fourier Transform Infrared). The present study focuses on the stability of γ-irradiated polymers used in single-use plastic bags made of multilayer films for the biopharmaceutical and biotechnological industries. The samples are irradiated at several γ-doses, up to 270 kGy, and compared with a non-irradiated sample used as reference. It shows that the γ-dose, the natural ageing up to six months and the γ-dose × ageing interaction are the most influential factors.