Aqueous Two-Phase Extraction (ATPE) is known to be a gentle separation technique for biochemical products due to the high water content of the aqueous two-phase system (ATPS) used. However, the phases' physicochemical properties like low interfacial tension, high viscosities and small density differences can lead to long phase separation times. This major drawback renders classical ATPE uneconomical for industrial application as additional equipment and energy is needed to promote faster phase separation. Our approach to enhance phase separation for ATPE is the Tunable Aqueous Polymer Phase Impregnated Resins (TAPPIR (R))-Technology, where one phase of an ATPS is immobilized inside porous solids, which are then dispersed in the other aqueous phase. A stable impregnation during TAPPIR (R) separation of the immobilized phase decides upon the competitiveness to classical ATPE and other protein recovery techniques. Therefore the impregnation stability dependent on the process (temperature and pH value), the properties of the particles and the physicochemical parameters of the ATPS was investigated. As many parameters need to be measured, making the determination of the impregnation stability predicting parameter difficult, the three-phase contact angle was proposed to describe the interaction of the ATPS with the porous solid. It was found, that the impregnability of phases and the impregnation stability could be predicted with the contact angle. Thus, the selection of the phase to be impregnated and the process design for novel separation tasks with TAPPIR (R) can be simplified.