<p>The rapid increase in plastic waste generation from industrial activities poses significant environmental impacts due to non-biodegradable nature of plastics. This research investigates the ability of utilizing post-consumer polyethylene terephthalate (PCPET) waste as a partial replacement for sand in sustainable construction materials. In specific, the research concentrates on enhancing thermal properties of eco-brick by exploiting low thermal conductivity. Thereby this research aims to improve sustainability of alternative building materials, evaluated through Life Cycle Assessment (LCA) and thermal comfort analysis. LCA calculations for eco-brick production utilized data from the Ecoinvent 3.9.1 database, with lifecycle modeling executed in OpenLCA software. The results highlight that eco-bricks with 1:2 ratio of washed polyethylene terephthalate (PET) exhibit the lowest environmental impact across categories namely global warming potential, ozone depletion and acidification. Remarkably, this 1:2 ratio of material composition (33.3% waste PET and 66.6% M-sand) yields a remarkable 126.67% reduction, and recycled brick aggregates show an impressive 182.22% reduction in carbon emissions compared to construction brick benchmarks. Conventional clay bricks achieve only a 68.89% reduction. For thermal comfort analysis, the eco-brick is tested using building design data under 4 ventilation options and 5 climate zones. In the view of sustainability of construction material, the produced eco-brick performs better than clay brick, fly ash brick, autoclaved aerated concrete (AAC) block, porotherm brick and gypsum block. The average difference between energy consumption considering each climatic zone and orientation is 42.47 kwh, for ventilation option 1, 48.45 kwh, for ventilation option 2, 42.42 kwh, for ventilation option 3 and 53.89 kwh, for ventilation option 4. This indicates that incorporating recycled plastics into building materials significantly improves the thermal properties.</p>