The drawability of polymer melts is of great importance for many polymer processes. Spinability can be determined by use of an ＇＇extension diagram＇＇: where the draw-down force needed for elongation of an extruded strand is measured as a function of drawdown speed. For this purpose, a tensile tester the so-called ＇＇Rheotens＇＇, was developed by Meissner (1971). It is well known that even small changes in polymer properties can lead to considerable changes in Rheotens diagrams. Also, the method is easy to use, shows excellent reproducibility and models industrial polymer processes like fiber spinning or film casting. However due to the complex prehistory of the polymer melt in the extrusion die, only qualitative interpretation of the Rheotens diagram was possible so far and draw-ability of different melts was compared on the basis of ＇＇melt strength＇＇ and maximum ＇＇extensibility＇＇. In the following we show that for thermo-rheologically simple polymer melts, temperature-invariant Rheotens mastercurves exist. We then prove the invariance of Rheotens mastercurves with respect to changes of the average molar mass. To substantiate our findings, Rheotens measurements on linear and branched polyethylene melts at different extrusion temperatures are presented. Rheotens mastercurves allow a direct and quantitative comparison of the drawability of polymer melts under processing conditions.