Polymers have been used in a wide range of applications ranging from fabrication of sophisticated medical equipment to manufacturing aircrafts. The design advantages of using polymers are its high strength-to-weight ratio, resilience, and compatibility with net-shape processes. In recent years, researchers have been trying to ascertain the mechanical as well as acoustical properties of polymers. Acoustical properties like attenuation of propagating ultrasonic waves through polymers vary in a broad spectrum depending on their chemical structure and stoichiometry. Guided wave techniques are widely used for nondestructive evaluation and inspection as well as examining the integrity of structures. This study demonstrates that guided wave techniques can be effectively utilized for material characterization, where efficient characterization depends on identification and selection of appropriate propagating wave modes and suitable signal processing techniques. The focus of this investigation is to estimate acoustic attenuation of acrylic (PMMA, polymethyl methacrylate), thermoplastic, using guided Lamb wave. Lamb waves are generated and received by piezo-electric transducers in a pitch-catch configuration. The received signals are first isolated from the inherent white noise using db4 based wavelet algorithm. The de-noised signals are then processed using Gabor Transform, which provides information about the group velocities of the propagating modes. The experimentally determined group velocities are compared with theoretical group velocities of the investigated polymers to identify the propagating Lamb wave modes. An effort has been made to estimate the attenuative properties of the thermoplastic from selective propagating Lamb wave modes.