This study focuses on some recent experimental results on the effects of the addition of glass beads to the linear and non-linear rheology, and hence melt processability, of two commercial shear-matched polyethylenes: an LDPE which shows strong strain hardening in elongational flow and an HDPE which does not. The beads were coated with a commercial coupling agent prior to blending with an extruder. The presence of the glass particles was found to raise the complex viscosity at all frequencies, but by different amounts depending on the frequency. The increase at low frequencies was predicted satisfactorily by the empirical Kreiger-Dougherty relationship for the low density polyethylene. The low frequency crossover, between G and G, was found to shift to lower frequencies with the addition of the glass beads. For the HPDE composites, the shift upwards in viscosity was lower than predicted by the KD model and also the shift of the G,G crossover was less than for the LDPE composites. The divergent results from the filled HDPE could be due to the different effect of the coupling agent on the properties of the neighbouring polymer. Non-linear measurements, in both shear and extension, were also carried out. The non-linear shear measurements reflected the same increase in viscosity as seen in the linear measurements at small strains. At higher strains the behaviour was different. This was particularly true for the filled LDPE composites tested in elongation, where the addition of the glass beads was found to severely suppress the strain hardening. It is expected that this is due to the development of cavities around the glass beads at higher strains, which we have seen in similar experiments on coupled glass beads in polystyrene.