K. W. N. S. Samaranayake et al., JSLAAS, Volume 1 (2018) 21 -31 21 Analysis of factors controlling acoustic absorption ofcommercial flexible polyurethane foams K.W.N.S. Samaranayake and R.V. Coorey * Department of Physics, University of Colombo, Colombo 03 Abstract In Sri Lanka, commercial flexible (CF) polyurethane (PU) foams are used for many purposes including sound absorption and noise reduction. The main factors that control sound absorption are thickness, density and flow resistivity of PU foam materials. The primary aim of the study is to experimentally determine frequency-dependant normal incidence acoustic absorption coefficients (NIAACs) of PU foams of densities in the range (12.0 kg m –3 to 21.0 kg m –3 ) and thicknesses in the range (5.08 cm to10.16 cm) of PU foam materials,using the impedance tube method according to ASTM C384-04 standard. The studied foam materials exhibit excellent acoustic properties with high NIAACs of more than 0.70 in the high frequency range above 1 kHz. For fixed density of these materials, NIAACs increased with increasing foam thickness. However, for fixed thickness of these materials, the NIAACs were found to be independent of the foam density. The air flow resistivity dependency on thickness and density of PU foams were determined based on simulated NIAACs as a function of frequency using the Dunn &Davern model. For fixed thickness of foam materials, the flow resistivity increased with increasing density of foam materials. However, for fixed density of foam materials, the variation between flow resistivity and thickness of foam materials were found to be inconsistent, indicating inhomogeneity / heterogeneity of CFPU foams. 1. INTRODUCTION A wide range of materials is used as sound absorption materials where it is necessary to reduce the noise and the reflected sound (Asdrubaliet.al., 2012).Materials which have nonporous solid surfaces, cannot absorb sound because the incident sound energy reflects back to the environment. However, if a surface is highly porous, the incident sound wave causes air molecules to vibrate within the cavities, channels, or pores present in these materials (Kuczmarski& Johnston, 2011) and lose some of its original sound energy. In the vibrational process, energy of air molecules is converted to heat due to frictional losses within the material (Arenas & Crocker, 2010). In porous materials, the pores can be either ―open pores,‖ * Corresponding author: Email: rvcoorey@gmail.com Keywords:absorption coefficients,Dunn & Davern, flow resistivity,polyurethane.