In melt mixed multiphase polymer blends, the mechanisms determining the spatial distribution and localization of solid particles smaller than the blend domain sizes are still not completely understood. From theoretical, considerations of a previous paper of one of the authors, it was derived that the transfer dynamics as well as the stability of different solid fillers at the blend interface reveal a strong dependence on the particle's aspect ratio. Low interfacial stabilities and high transfer speeds between the blend phases can be deduced for fillers with very high aspect ratios, entitled as the "Slim-Fast Mechanism" (SFM). The SFM appears suitable to explain in retrospect important features of several previous studies that address the localization of differently shaped nanoscaled particles in polymer blends. The SFM was evaluated by investigating the simultaneous transfer of multiwalled carbon nanotubes (MWCNTs) and carbon black (CB) from a poly(styrene acrylonitrile) (SAN) precompound into the thermodynamically preferred initially unfilled polycarbonate (PC) phase during melt mixing.