The most important quality attribute in roll compaction/dry granulation is the ribbon porosity, as it predominantly determines the granule porosity and granule size distribution. The porosity, however, is not distributed homogeneously over the ribbon. In this study the porosity distribution was investigated using X-ray micro-computed tomography and demonstrated that characteristic distribution patterns exist over all three spatial directions, the ribbon length, width, and thickness. In detail the distribution patterns depend on the sealing system.