We utilize Brillouin light scattering to investigate the shape-persistence of polystyrene-silica core-shell Particles by recording their vibrational eigenmodes as a function of temperature. The thin silica shell (tens of nm) protects the polymer Core from changing its spherical shape at temperatures above its glass transition temperature T-g, readily obtained from the same experiment. The rigidity of the confined core is enhanced compared to the bare core. (C) 2009 Elsevier Inc. All rights reserved.