AbstractIn previous studies, we discussed the use of water as an environmentally benign blowing agent for foaming of polystyrene beads, resulting in so-called WEPS, viz. water expandable polystyrene foam. Several grades of precursors to WEPS have been prepared by varying the water content and the molar mass, to control the melt strength of the polystyrene matrix. Additionally, we have used (endcapped) poly(2,6-dimethyl-1,4-phenylene ether) (PPE) to control both the meltviscosity and the glass transition temperature Tg. The advantage of using the blend PS/PPE is that the processing window for foaming is increased in view of the difference between the Tg and the boiling point of water. Using the novel WEPS route with some adjustments, for the first time a water expandable homogeneous blend of polystyrene and end-capped PPE was successfully obtained.