Polyethylene Terephthalate (PET), known as plastic, is the most widely used product in the world today. However, the increase in the amount of imperishable plastic waste is a concern today. Repurposing of plastic waste in useful products such as concrete appears as an alternative in the construction industry. This paper’s main objective is to explore the performance of thermal properties in concrete by incorporating waste Polyethylene Terephthalate (PET) as an aggregate in a concrete mix. Other than reducing energy usage in buildings, reusing waste PET should introduce an improvement in friendly waste management. Laboratory experimental analysis was done by measuring the parameters of thermal conductivity on four types of concrete design mix which includes 0% PET, PET 5%, PET 15% and 25% PET in concrete block. Finally, an implementation of a sustainable approach to these new concrete materials; the obtained results highlight their mechanical properties of enhancement in thermal property, which reduces heat gain and achieve better thermal insulation compared to a traditional concrete mixture with a similar application of test type. This implementation has been proved to optimize efficient thermal performance towards sustainable building material.