Compacted, macroporous complexes of poly(styrenesulfonate) and poly(diallyldimethylammonium) were dehydrated under defined osmotic stress using poly(ethylene glycol), PEG. A strong mechanical response to dehydration was observed. At the lowest osmotic stress applied, macropores within the complex were compacted, and the material became transparent. With additional osmotic stress, the decrease in water content with increasing stress slowed considerably, but the complex became much stiffer, the equilibrium modulus reaching several hundred MPa. Concurrently, the complexes became more brittle. Multi layers of the same polyelectrolytes reached equilibrium hydration levels much faster and also increased significantly in modulus. Using an empirical fit, the plasticizing efficiency of water was shown to be exceptionally strong.