A testing instrument and method for measuring the intrinsic strength of polymeric materials via cutting includes a pair of mechanical clamps connected at a base to low-friction hinges. The clamps are configured to secure the elongate edges of a polymer specimen, and to periodically load the specimen to a predetermined strain. The load on the specimen while strained is measured with an opening force load sensor. While in the strained condition, the specimen is cut with a highly sharpened blade, and the cutting force also measured by a cutting force load sensor. A cutting energy curve may be plotted from these measurements, from which a cutting energy can further be derived.