Potassium‐oxygen batteries (KOB) are a promising energy storage technology with high theoretical energy of 935 Wh/kg and long cycle life. Potential applications require the development of affordable cathode materials with high practical capacity. In this article, we show that low‐cost polytetrafluoroethylene (PTFE) treatment increases the discharge performance of a commercial carbon paper cathode. Cross‐sectional scanning electron microscopy reveals that PTFE alleviates mass transport limitations and facilitates homogeneous deposition of the discharge product potassium superoxide (KO2) within the cathode pore structure. Using electrochemical impedance spectroscopy, we found that PTFE, in combination with the appropriate electrolyte volume, can prevent pore flooding by the electrolyte. Free volume permits fast, gaseous oxygen transport throughout the cathode, which lowers mass transfer resistances and improves the rate capability. Moreover, PTFE enables high pore volume filling by KO2 and, in turn, high discharge capacity. Our results demonstrate that controlling the mass transport is essential for high‐performance cathodes for KOB.