The use of acoustic cavity fillers or “baffles” to prevent the propagation of air borne and structure borne noise, water and dust into the interior spaces of vehicle structures has been in practice for many years. Continuous development of new OEM requirements has pushed the state of the art concerning the design and functionality of these cavity sealing systems. Various technologies are available to OEMs to provide sealing that will prevent water and dust penetration, maximize performance of vehicle HVAC systems, and minimize the propagation of noise from the body structure into the interior compartment under operating conditions. Generally, three types of cavity sealing systems are available: pre-formed thermoplastic-based systems that incorporate a heat reactive thermoplastic sealer applied to a nylon or steel “carrier” for attachment to the body structure; heat reactive rubber-based sealer systems that incorporate a carrier, push pin or pressure sensitive adhesive layer for attachment; and bulk applied chemically reactive two component polyurethane or expandable “foam” systems. In this case study, a challenge undertaken by this supplier was to provide a thermoplastic baffle design of equal or lesser weight compared to a competitive, die-cut rubber-based technology currently in production at a particular OEM, while achieving equivalent acoustical performance. This paper will document the alternative design proposals and development activities that were pursued to meet this particular objective.