<p>Polyhydroxybutyrate (PHB) is a biodegradable polymer derived from renewable resources, offering similar mechanical properties to petrochemical polypropylene. However, the surface properties needed for a wide range of applications are demanding and require controlled treatment. Appropriate surface modifications, such as the application of thin functional layers, can change and improve their characteristics. A promising approach involves the deposition of thin amorphous hydrogenated carbon (a-C:H) layers via low-temperature radio frequency plasma-enhanced chemical vapor deposition. This can tailor surface properties such as wettability and the chemical composition. Both are influenced by the sp²/sp³ carbon bond ratio, which in turn depends on the angle of plasma incidence. Accordingly, changing the coating geometry also changes layer properties. Here, PHB films were coated with a-C:H layers at different angles and with different thicknesses. Scanning electron and atomic force microscopy recorded the surface morphology, while contact angle goniometry was used to determine the wetting hysteresis and the surface free energy. Results show that increasing layer thickness reduces the variability in contact angle hysteresis. Surface-sensitive synchrotron-assisted spectroscopy and specular reflection IR spectroscopy revealed angle-dependent variations in the sp²/sp³ bond ratio, confirming a direct correlation between coating geometry and surface chemistry.</p>