Micro and nano sized features on surfaces enable new product functionalities. On the lab scale, this has been demonstrated for many applications e.g. for devices with tailored optical or mechanical properties. When process steps are scaled-up in order to establish high volume production, special care must be taken to guarantee the quality of the work pieces. When using (compression) injection moulding for mass production the melt viscosity is a key parameter to achieve good product qualities. In this paper, the impact of water absorption on melt viscosities and work piece qualities is evaluated. Qualitative and quantitative results are presented for micro needle arrays which are produced on the IMPRESS platform (compression injection moulding machine in combination with several peripheral modules).