The automobile's interior acoustic treatment must provide sufficient sound absorption to enhance the conversational ability between the vehicle's occupants under all driving conditions. Addressing this increasingly important customer driven requirement becomes even more challenging in larger vehicles like minivans. Several factors affect clear conversation (Speech Intelligibility) and include: the reverberation/absorption characteristics of the environment and the type and intensity of ambient noise. This paper discusses the effects of major interior trim components on the reverberation characteristics of a minivan interior environment and their impact on speech intelligibility. Among interior trim components, seats have been found to be the major contributor to a vehicle's interior sound absorption. Various component and in-vehicle test results are presented to exemplify the effects of seat constructions on speech intelligibility. Additionally, proposed bench-top test criteria are discussed to provide guidelines for seat construction to improve speech intelligibility.