We herein present the development of inkjet inks that have the capability of producing micro-scale polyurethane foams. Inkjet technology can be used as an additive manufacturing tool using small amounts of liquids to form a desired structure. Furthermore, in situ chemical reactions can be carried out using this particular printing technique. In order to achieve suitable printing inks, viscosity properties were taken as the key limiting factor choosing the ink components. Poly(ethylene glycol) 200 was selected as the main polyol for the reactive inks. Glycerol ethoxylate, also known as star-PEG, was selected as the crosslinking agent due to its three primary hydroxyl groups as well as its good compatibility with PEG200. Variation in star-PEG content was investigated by means of rheometric and tensiometric measurements. For the reactive isocyanate compound, 1,6-hexamethylene diisocyanate (HDI) was chosen due to its high reactivity and low viscosity. Polyurethane foams (PUF) were prepared in bulk to validate the foam recipe. Small droplets of the inks were then tested by manually placing two drops on top of each other. It was shown that in the absence of mechanical mixing the gelling and blowing reaction still take place. Furthermore, catalytic influences on the reactions were investigated using a central composite experimental design combined with FTIR-ATR spectroscopy. In order to evaluate the spectra, a deconvolution of the Amid I and Amid II area was conducted. The results were evaluated using an analysis of variance to gain models.