Cardiopulmonary resuscitation (CPR) is an emergency course of action developed to sustain oxygenated blood flow in persons suffering from cardiac arrest by manually compressing the heart in the chest and providing rescue ventilations. The best-selling CPR manikins, an integral part of training, lack biofidelic characteristics in appearance, feel, and response, and as a result, the rescuer's learning experience suffers. The objective of this thesis was to test the compressibility properties of different foams and thermoplastics in order to determine which material would most accurately imitate a human chest response. The results suggested that styrene-ethylene/butylene-styrene (SEBS) was the best choice, because its increasing stiffness under increasing compression was characteristic of a human chest cavity. Further testing must be done to determine the best composition of SEBS, analyze its response under cyclic compressions, and improve its durability.