The invention relates to a composition comprising a rubber-modified monovinylaromatic polymer comprising: 70 wt % or more of a monovinylaromatic polymer matrix, from 2 to 12 wt % of at least one rubber, and from 0.1 to 3.4 wt % of metallocene-catalyzed poly-alpha-olefins (mPAO) all based on the total weight of the rubber-modified monovinylaromatic polymer, with the mPAO having a kinematic viscosity of at least 950 mm2/s at 40° C. and at most 2,000 mm2/s at 40° C. as measured according to ISO 3104. The invention also relates to articles made from such composition and to the process to produce said composition and said articles.