This dataset comprises the outputs from nine firn models at four sites of the Greenland ice sheet produced for the firn meltwater Retention Intercomparison Project (RetMIP). The nine models were forced by the same weather-station-derived mass and energy fluxes. The simulated firn density, temperature, liquid water content, refreezing rates and ice fraction are interpolated on the same grid from the surface down to 20 m deep with 10 cm vertical resolution. For each three-hourly time step, the total firn air and water content, total refreezing and total runoff simulated in the entire firn column are also calculated for each model. For one of the sites, Dye-2, two simulations are provided: one spanning over 17 years and one restricted to the 2016 melt season using a more recent weather station for the forcing. The forcing data for these model runs are available here: Vandecrux, Baptiste, 2020, "The firn meltwater retention model intercomparison project (RetMIP): forcing data", https://doi.org/10.22008/FK2/GZ3CSN, GEUS Dataverse, V1