In this letter, a hydrogel compression method for the facile generation of high polymer concentration within single giant unilamelar vesicles (GUV) is presented. A GUV with an internalized poly(N-isopropyl acrylamide) solution is heated above the lower critical solution temperature (LCST) until compartmentalization by collapsed hydrogel microaggregates occurs. Subsequently, the volume of the vesicle is decreased by reducing the area of the enclosing membrane. An increase in concentration by a factor of up to 11 is reached while the membrane remains intact, bringing the model system close to the living cell situation with its high concentration of proteins in the cytoplasm. The polymer-filled vesicles are also ill a suitable density range to significantly improve the flow control performance of hydrogel valves embedded in soft matter nanofluidic devices.