It has been discovered that the melt instability of styrenic polymers, particularly high impact polystyrene (HIPS) can be reduced or eliminated by the blending therewith of a relatively high melt flow index (MFI) material, such as polystyrene homopolymer. Draw resonance of the melt blend can also be reduced by this method, thereby improving melt processing of these materials. A method to measure melt instability of drawn materials is also discussed.