The ribbon relative density is one of the key quality attributes during roll compaction/dry granulation, as it primarily determines the granule porosity and granule size distribution. In this study, a new approach to measure the ribbon relative density in-line was investigated. A thermographic camera was used to record freshly produced ribbons as they left the gap. In a first step a principal correlation of the measured ribbon temperature and the ribbon density was proven. Furthermore, the cooling rate after compaction was identified as an additional characteristic that can be used to determine the ribbon density. Interestingly the thermographic images also revealed temperature distributions within the ribbon that could be matched with density distributions measured by X-ray micro-computed tomography. In the following, additional characteristics that are equally important for the practical application as an in-line measuring tool were further investigated. The technique showed short reaction times to changes in the process and in a long term experiment no temperature drift over time could be detected. This study demonstrated the applicability of a thermographic camera as an in-line analytical tool for the determination of ribbon relative density. (C) 2017 Elsevier B.V. All rights reserved.