Certain molecules act as biomarkers in exhaled breath or outgassing vapors of biological systems. Metal oxide gas sensors are of great interest to detect these molecules. However, often they are not selective enough to identify the specific molecules. In addition, they typically lose their excellent performance at high humidity levels. In this study nanoscale polytetrafluoroethylene (PTFE) thin films deposited via solvent-free initiated chemical vapor deposition (iCVD) were investigated as a possible pathway to tune the selectivity of metal oxide gas sensors as well as hydrophobic surface functionalization. The gas-sensing properties of two types of PTFE-coated gas-sensing structures are measured for this purpose at several operating temperatures. The first structure is a thermally annealed TiO2 film while the second structure is a thermally annealed TiO2 film with an additional CuO film. After the deposition of the iCVD PTFE thin films the structures exhibit a high response and excellent selectivity to 2-propanol vapor. The experimental data presented here, promote the use of such PTFE-coated gas sensing structures as reliable, accurate and selective sensor structures for the tracking of gases at low concentrations. This enables new possibilities in application fields like biomedical diagnosis, biosensors, and the development of non-invasive technology.