This study examined the hydration state of the PEM and GDLs in four PEM fuel cells, with various combinations of SGL Carbon carbon paper GDLs with different PTFE loadings, in response to current step up and step down transients. The goal was to determine the effect of these GDLs and their PTFE loadings in the substrates and MPLs on the water dynamics and performance. The fuel cells used GoreTM MEAs and were operated at 80oC with stoich tracking gas flows at 50% inlet RHs. In situ HFR measurements were used for monitoring PEM hydration and in situ neutron imaging of the fuel cells was conducted at NIST with quantitative analysis to determine the liquid water content in the GDLs and channels. High PTFE loadings in the porous, open GDL substrates allow for greater water flux and lower water holding capacity, which facilitates cathode reaction water removal at high currents. In contrast, high PTFE loadings in the less porous, smaller pore size MPLs increase the water barrier attributes and seal in PEM water. Counter flow gas feed results in more even water distribution than co-flow feed. Counter flow feed with cathode air flowing against gravity increases cell hydration in dry operating conditions.