Comparisons between characteristic lengths and fibre equivalent diameters in glass fibre and melamine foam materials of similar flow resistivity

Flow resistivity, tortuosity, viscous characteristic length and thermal characteristic length of three melamine foam and two glass wool samples have been measured. It has been found that a melamine foam sample with a bulk density 10.3 kg m−3 and a glass wool sample with a bulk density 28.0 kg m−3 have almost the same flow resistivity, however, the bulk density is as much as three times different. The cross-sectional pore shape factors, which are deduced with the non-acoustical parameters in the Johnson–Allard model, of the melamine foam are smaller than those of the glass wool. This paper also discusses a new relationship between the flow resistivity, the fibre equivalent diameter and the bulk density in melamine foam.