Natural fiber-reinforced cement mortars do not always have lower sound transmission loss (STL), which means their sound insulation performance varies depending on several factors. The type of natural fiber, its content, and how it interacts with the cement matrix all influence acoustic behavior. Some fibers, like coir or hemp, can enhance sound absorption by increasing internal porosity and scattering sound waves, which may improve sound insulation at mid to high frequencies. However, these same porous structures can reduce overall density, potentially decreasing STL and allowing more sound to pass through at lower frequencies.

In general, while natural fibers may enhance sound absorption (useful for reducing echo or reverberation), they do not always improve sound insulation (blocking sound from passing through). If the inclusion of fibers significantly lowers the density or creates continuous air pathways, STL may decrease, especially for low-frequency sound. On the other hand, optimized designs—such as using multiple layers or combining with dense backing materials—can offset these effects and maintain or even improve sound insulation. So, the impact of natural fibers on STL depends on the specific design and composition of the mortar.

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