The extensional flow mixer (EFM) has been used in industry, for e.g., homogenization of reactor products, polymer blending, incorporation of plasticizer, etc. Recently, several laboratories attempted to use EFM for dispersing organoclay in a molten polymer. Thus, usually EFM was mounted on a twin-screw extruder equipped with a gear pump. The use of EFM resulted in improved dispersion and performance - more significant in polyamide or thermoplastic polyester-and marginal in a polyolefin or polystyrene. Recently, to improve EFM efficiency, the commercial EFM-3 was modified by redesigning the convergent-divergent plates that engender the extensional flow. The two mixers, EFM-3 and the new EFM-N, were evaluated using a single-screw extruder. Two systems were examined: (1) polyamide-6 (PA-6) with Cloisite(R)-15A (C15A) and (2) polypropylene with maleated-PP and C15A. The compounded samples were injection-molded, and then tested for the degree of dispersion and mechanical performance. The results showed superiority of EFM-N. Compounding PA-6 with C15A in a single-screw extruder with EFM-N exfoliated the organoclay, producing polymeric nanocomposites with high performance, comparable or better than that of a commercial nanocomposite produced by polycondensation of epsilon-caprolactam in the presence of clay, preintercalated with reactive cations.