Sustainable materials like paperboard can substitute for crude oil-based polymers in packaging applications and, by doing that, reduce the negative environmental impacts caused by plastic waste. For a broader application in the packaging industry, the forming of paperboard needs to overcome its limited forming behaviour and barrier properties. The presented work aims to influence the forming behaviour of uncoated and polyethylene terephthalate (PET)-coated paperboard with additives like water, gelatin and soap. Furthermore, the differences in the mechanical behaviour of coated and uncoated materials are investigated. For the studies, tensile, bulge and forming tests were combined with different optical measurement methods. The investigations showed that the overall forming behaviour is affected by the mentioned additives and can be improved. Additionally, the interaction of the coating and substrate paper is investigated under different load conditions.