The energy loss through building components resulting in higher energy consumption, thus energy saving has become an essential aspect in design and comfort. This study aims to optimize the thermal insulation of red clay bricks used in the walls of buildings by using a multiscale method. The finite element approach in ABAQUS software has been used to simulate the bricks under different configurations and conditions. Due to cost and time challenges and difficulties in simulation and complex calculations, simplified and applicable equations have been derived to calculate thermal insulation properties. The results show that the paper’s brick design has a significant thermal conductivity reduction that could reach more than one-third of the other corresponding studies. The study goes to fill the hollow bricks by the insulation polyurethane foam (PUF) and comparing the results with air hollow bricks. Besides its other advantages, the outcomes reveal that using the PUF has a noticeable desired-influence in thermal insulation when considering the heat transfer by convection and radiation inside the air cavity of bricks.