Elongational and shear viscosities of bead‐filled styrene acrylonitrile composites were measured in the rubbery flow region at very low strain rates. Composites contained 9–37% spherical glass beads by volume. Within experimental error, elongational viscosity was found to be constant and equal to three times shear viscosity at very low strain rates for the composites containing less than 20 vol % glass beads. The experimental data were used to evaluate a number of the classical theories for the viscosity of suspensions. In general, the theories were more appropriate for the elongational than for the shear data. Both elongational and shear viscosities were discovered to have the same dependence on the filler concentration up to 20 vol % glass beads. Dewetting is very noticeable in high strain tensile testing for all nonzero filler concentrations. In the data presented here, simultaneous measurements of longitudinal extension and lateral contraction established that the samples did not dewet during the viscosity measurements.