Thermal performance in very low density fibrous composites depends on density, fiber diameter, fiber diameter distribution, fiber orientation, and fiber distribution, among other factors. Acoustical impedance of these products, while the physical phenomenon is not the same, depends on the same factors. Because of this, the two properties show a high degree of non-causal correlation. Each property may be the functional property of interest for the product, or the property may be measured and analyzed as a means to understand the relative contributions of the different controlling factors. However, sample to sample variation in a disordered composite such as building insulation is very high. Therefore, when studying fiber orientation and distribution, the density variation from sample to sample may obscure the effect of fiber orientation on thermal or acoustical properties. For this presentation, 8x8x8 inch cubes of insulation were measured in three spatial orientations, thus fixing the total density, fiber diameter, and fiber diameter distribution of each sample. At the same time, the individual fiber orientation as well as the distribution of fiber mass relative to the direction of heat or sound propagation is effectively changed.
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