Measurements of the porosity of three polar firns were conducted in the 1990s by Jean-Marc Barnola using the method of gas pycnometry. From these data, a parametrization of firn pore closure was produced and used in different published articles. However, the data have not been published in their own right yet. We have made the data publicly accessible on the PANGAEA database and here propose describing how they were obtained and used to produce the pore closure parametrization.