Elongational thinning is observed in model polypropylene/polystyrene (PS) blends filled with nanoparticles at nanoparticle loadings >= 3 vol. % and high strain rates, wherein the nanoparticle network that forms at rest is destroyed by the deformation. The elongational thinning is stronger in blends with hydrophilic silica surfaces than with hydrophobic silica, apparently due to stronger interaction within the hydrophilic silica network and between PS and hydrophilic silica. Moreover, the elongational deformation of droplets is not significantly altered by the addition of hydrophilic silica at lower silica loadings but nearly completely inhibited at higher loadings. In contrast, hydrophobic silica significantly boosts the deformation of droplets in elongation possibly because of the reduced interfacial tension due to the preferential distribution of hydrophobic silica at the droplet-matrix interface, relative to the hydrophilic silica which resides mostly in the PS matrix. (C) 2017 The Society of Rheology.