A biaxially oriented thermoplastic structure including a low density core layer formed from polypropylene, highly crystalline polypropylene or high density polyethylene, and outer layers formed from highly crystalline polypropylene or high density polyethylene. The thickness of the core layer is about 60 to about 95% of the overall thickness of the structure. The stiffness of the structure in the machine direction is in a range from about 0.015 to about 0.15 pound force-centimeters.