The SRL UW Panel Element Tester is an advanced apparatus that can apply arbitrary combinations of in-plane stresses to thin membrane specimens (standard specimen dimensions: 3’ x 3’ x 3’’). The testing rig includes a stiff steel reaction frame, 37 60-kip hydraulic actuators (with 8’’ stroke), and three rigid links and it is served by a 10,000 psi hydraulic pump. It is equipped with four hydraulic lines (channels), each comprising banks of 10 actuators. Its independent controller uses proportional valves to regulate the pressure in each line. Load cells and pressure transducers are used to control forces and pressures that develop in the actuators. The tester is the first of its kind to be available on the west coast of the U.S. and it is unique among similar testers for its flexibility in terms of stress states that it can generate.