AbstractThis study demonstrates the potentials of using Cuttle Bone Powder (CBP) as a biofiller and a low-cost sustainable alternative to cement for the production of lightweight Foamed Mortar (FM). The effects of varying Foam Volume (FV), as well as cuttlebone powder at various particle sizes (fine and coarse) and cement replacement ratio (5%, 10%, 15%, 20%, and 25% by weight) on the physical, mechanical, thermal, and durability properties of foamed mortar, are experimentally investigated. Results show that the inclusion of cuttlebone as cement replacement under moist curing showed decreased density with minimal reduction in strength with increasing foam volume. Besides, to enhance the hydrophobic behavior of the foamed mortar, Zinc Stearate (ZnS) at 1% (by weight of cement) was used in foamed mortar which decreased the water absorption and sorptivity. The thermal conductivity values also slightly decreased with increasing cuttlebone replacement. With the beneficial effect observed on the density and strength performance and from the cost analysis, cuttlebone as cement replacement with ZnS addition is recommended for the production of low-cost sustainable hydrophobic foamed mortar.