Abstract: A spinning drop tensioextensiometer provides for the ability to rotate a tube carrying two different polymers, under conditions which keeps the polymers melted, and which causes the less dense polymer to form a drop of a generally cigar shape. By measuring the diameter of the drop at desired angular velocities upper and lower bounds for interfacial tension can be determined. Further, these bounds define relaxation curves for the extensional relaxation of a blend of two polymers. The polymers are placed in a glass tube that is rotated at high speed within an oven that has an opening through which the diameter of the inner polymer drop can be measured utilizing optical equipment, such as a video camera projecting an image onto a monitor.