We report on the changes of the Sun's subsurface stratification inferred from helioseismology data. We used SOHO/MDI (SOlar and Heliospheric Observatory/Michelson Doppler Imager) /-mode frequencies and their temporal variation for the last 10 years to compute the variation of the radius in the subsurface layers of the Sun by applying helioseismic inversions. We have found a variability of the "helioseismic" radius in antiphase with the solar activity, with the strongest variations of the stratification being just below the surface around 0.995R⊙. Besides, the radius of the deeper layers of the Sun, between 0.975 R⊙ and 0.99 R ⊙ changes in phase with the 11-year cycle. These results imply a non-homogeneous variation of the radius with depth and time.