The firnificaton of dry polar snow has been investigated with the means of X-ray micro-computer tomography (CT). The measurements were carried out on shallow firn cores and snow pit samples during the field campaign 2005/2006 at the EPICA (European Project of Ice Coring in Antarctica) DML-drill site, Antarctica. The CT-devices have been successfully tested in the field and offered us a novel method to study the fragile three dimensional structures of deposited snow and firn.In this presentation we focus on the evolution of pore/ice cluster sizes and on the development of intergranular bonding. The parameters are derived from volume image analysis of the three-dimensional CT-reconstructions. We show that the number of bonds per cluster in samples near the surface is highly correlated to their respective density. Accordingly, the neck radii are anticorrelated to the density. Maxima of pore size and anisotropy are observed at depths where the metamorphism is dominated by temperature gradients. The relevance of experimental findings is discussed in relation to recent firnification models.