Meltwater retention in the firn layer of the Greenland Ice Sheet is has the potential to buffer sea level rise due to ice sheet melt. The capacity of the firn layer to store meltwater is unclear, however, because refrozen ice layers can act as impermeable barriers to meltwater percolation, promoting runoff rather than retention. We present time-domain reflectometry and thermistor data which demonstrates that meltwater successfully penetrates ice layers up to 12 cm thick in the near-surface firn at Dye2, Greenland. Our observations indicate that ice layers within polar firn can become permeable when summer warming and latent heat release from refreezing meltwater raise temperatures to the melting point. This facilitates meltwater retention, and indicates that the depth of penetration of the summer melting front (the 0°C isotherm) represents the primary control on meltwater infiltration in the percolation zone of the Greenland Ice Sheet.