The break-in of a Proton Exchange Membrane (PEM) fuel cell brings the performance to a maximum and stable level and is crucial for industrial applications. An optimal break-in procedure maximizes performance in minimal time while preventing degradation. However, the development of an optimal break-in lacks an understanding of triggered electrochemical and physical processes. We use polarization curves and Electrochemical Impedance Spectroscopy (EIS) to compare three promising break-in methods, constant voltage break-in, voltage cycling, and cathode starvation, regarding their capability to increase performance. The triggered electrochemical and physical processes inside the interface between cathode catalyst layer and the membrane are revealed by impedance data. The impact on durability is investigated using Cyclic Voltammetry (CV) and hydrogen crossover measurements. The resulting insights into processes inside the fuel cell during different break-in methods lead to an optimal break-in which saves time, hydrogen, and therefore money in PEM fuel cell production.