Firn cores BAL-1 and PASO-1 were both retrieved in November 2015 from the Union Glacier region, located in the Ellsworth Mountains at the northern edge of the West Antarctic Ice Sheet. BAL-1 was drilled in a U-shaped glacial valley (Balish Glacier) at an altitude of approximately 1520 m above sea level (a.s.l.) to a depth of 17.28 m. PASO-1 was drilled on a plateau west of the Gifford Peaks at an altitude of about 1920 m a.s.l. to a depth of 15.04 m. Both firn cores were obtained using a portable solar-powered and electrically operated ice-core drill (Backpack Drill; icedrill.ch AG). Density measurements of the two firn cores were performed at the ice-core processing facilities of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven, Germany, in spring and autumn 2016. X-ray microfocus computer tomography (ICE-CT; Freitag et al., 2013, doi:10.3189/2013JoG13J028) was used for the measurements, providing depth-density profiles with a resolution of better than 1 mm. The density data were used to analyse the firn core stratigraphy (e.g., determination of the snow-firn transition depth, identification of wind crusts), to calculate diffusion lengths as well as to derive accumulation rates for the firn-core drill sites.