The consideration of filter density as a filter design parameter has increased in recent years. Traditional filter design is based on pressure drop or resistance to draw to achieve specified smoke filtration levels (example NFDPM). Pressure drop is related to the acetate fiber surface area which filters main stream smoke. Filter density does not necessarily correlate with fiber surface area. For example, changing the filter length will not change the density but has a significant impact on filter pressure drop (fiber surface area). Additionally, under or over processed the tow has an impact on filter density and filter pressure drop. Incorrectly processed tow is easily detected by filter pressure but filter density is an unproven parameter. This poster will illustrate the impact of the filter physical dimensions, plug wrap paper thickness, tow item, and tow processing on density and pressure drop. Under certain conditions filter density may be an appropriate way to model filter performance but may not be suitable under all conditions.