Hearing protection devices (HPDs), a widely used countermeasure against noise-induced hearing loss, are laboratory-tested for their attenuation (noise reduction) capabilities. Unfortunately, laboratory tests overestimate the in-workplace performance of the devices, potentially leading to inadequate protection for the user. Many factors affect in-field effectiveness, including the physical design and "wearability" of the protector. Wearability, a highly subjective aspect which encompasses such characteristics as user comfort, ease of use, and acceptability, directly affects performance by influencing the regularity of use and the manner in which a protector is worn. This research investigated the influence of the user's work-related activities over a prolonged wearing period, and of variations in headband compression force and cushion material (liquid- or foam-filled) on achieved noise attenuation and wearability (comfort and acceptability) of earmuff hearing protectors. REAT (real-ear attenuation at threshold) testing procedures were used to collect attenuation data on 24 subjects, both prior-to and following completion of a simulated work task. Bipolar rating scales were utilized to collect pre- and post-task wearabi1ity data. Statistical analyses demonstrated that the work-related movement and wearing time significantly reduced achieved attenuation and, for higher compression earmuffs, also degraded perceived comfort and acceptability. A high headband compression force was 1inked to increased attenuation and to poorer user comfort and acceptance. The data revealed no significant difference in achieved attenuation or wearability between cushion types. The results illustrate the powerful influence of physical activity on HPD effectiveness and the criticality of certain earmuff design parameters to both attenuation and wearability. Furthermore, the existing tradeoff in earmuff design between comfort and attenuation was clearly demonstrated. / Master of Science