The use of biodegradable and compostable plastics in packaging aims to address environmental concerns associated with single-use plastics, but their fate under environmental conditions was little studied. The objective of our study is to investigate the physical and chemical changes occurring when these materials are subjected to composting and UV ageing processes. We focused on two biodegradable films (PBAT, ethyl cellulose) and compared them to conventional polyethylene films. Our results revealed chemical changes via FTIR and pyrolysis-GC/MS and partial degradation, which is specific to the plastic type.