Many commercially available indoor air filters are currently being marketed with tackifier filter adhesives applied to the surface of the fibres or to the face of the filters, However, little information is available in the literature concerning the application of these tackifiers, and their effectiveness in reducing particle penetration through filters. It is of scientific value to investigate the efficacy of such tackifiers, especially in the light of increasing concern for indoor air quality, The paper presents the ongoing results of an investigation in which polypropylene melt-blown media were manufactured under a variety of operating conditions, to produce media which might be suitable for use in indoor air quality filters, The filter media were prepared at the Textiles & Nonwovens Development Center (TANDEC), and tested for filtration efficiency in the Air Quality Laboratory housed in the Department of Civil & Environmental Engineering at the University of Tennessee, Knoxville, Efficiencies were determined using both cold, polydispersed dioctylpthalate (DOP), as well as monodispersed latex particles (0.6 to 3.0 mu) using an ASTM 1215 filtration test stand. The objectives of the research were to determine the initial efficiency of the media at velocities ranging from 3 to 375 cm/s, and to compare the measured results with filtration theory, At the higher velocities, typical of those used in indoor air filters, the experimental efficiencies using dry particles were significantly less than both the DOP and theoretical efficiencies, because of the kinetic energy of the particles, which resulted in particle bounce. Empirical corrections were developed as a function of the kinetic energy to account for the decreased efficiency resulting from particle bounce, and are presented. Tests were also conducted on a melt-blown medium in which the fibres were coated with various loadings of a tackifier, referred to here as being ＇topically＇ applied, The results showed that the efficiencies at high velocities were improved as a result of the reduction in particle bounce, while the efficiencies at low velocities were unchanged even though larger effective fibre diameters resulted from application of the tackifier.