Experimental access to the charge exchange dynamics inside a solid is typically hindered by the lack of temporal resolution of ion scattering experiments, wh.ich must be in the femtosecond range to address charge transfer, excitations and de-excitations. An indirect approach to the ion's charge exchange is to observe the emitted secondary particles and to link their energy spectra to modelling calculations, which inherently contain major uncertaintie [l]. Another way is to measure the ion after the interaction with a solid and therefore determine the charge exchange directly. Grazing scattering experiments were conducted earlier, but in this case the ion is typically not entering the solid but is scattered above the surface and the interaction time can easily be very long resulting in mostly neutralized atoms in the experiment [2]. Here we present experimental data on charge exchange of slow highly charged ions at various veloci- ties in single and multi-layers of freestanding graphene [3]. From a careful analysis of the variation of charge after transmission through the solid as function of the velocity and material thickness we find that the charge decreases exponentially with time spent inside the solid and the neutralization time constant is linearly dependent on the initial charge.