By adding only about 1% of soft polymer nanoparticles to natural rubber, a dramatic decrease in the viscosity (more than 50%) is induced. Our recent time of flight measurements on a model system (well-characterized poly(ethylene oxide)(PEO) with poly(methyl methacrylate) (PMMA) nanoparticles) show on the contrary slowing down of the PEO dynamics in the presence of soft nanoparticles. We want to use IRIS to explore an extended dynamic window towards longer times in order to better understand these unusual behavior and its origin.