Mechanical properties along with eco-friendliness make the natural fiber reinforced composites suitable alternatives to the synthetic materials. But for structural integrity, the ply-layer combinations must be optimized, because more ply-layers could enhance mechanical strength and thermal stability but may increase moisture sensitivity via hydrophilic fiber content. In this context, the effects of ply-layers on the sisal fiber (SF) and flax fiber (FF) reinforced epoxy hybrid composites’ mechanical, thermal, and water absorption (WA) properties have not been checked yet. Therefore, present study aims to find the effect of ply-layers on mechanical, thermal, and WA behaviors of laminated hybrid composites consisting 4, 8, 12, and 16-layer combinations of SF and FF mats reinforced (equally ply-numbers) in epoxy matrix (52vol%). A hand lay-up and hot-compression created laminated hybrid composites. The 8-layer composite performed superior, achieving 88.13 MPa tensile strength, 190.52 MPa flexural strength, and toughness >200 MPa√m. FTIR established fiber-matrix chemical bonding. WA of the 4–16-layered hybrids varied to 0.764%–2.385%; however, their water contact angle increased from 78.36° to 110.45° while thermal stability was retained up to 240°C. Here, the 8-layer configuration represents the optimal design, balancing mechanical load transfer with manageable WA (1.959%). Hence, SF/FF/epoxy hybrids can be used in sustainable green-composite engineering and prosthetic applications.
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