|Ceramic brick as building material has been used for thousands of years. Nowadays, the energy performance of new products has to meet rigorous requirements; therefore, in the design of new ceramic masonry blocks, building physical simulations are essential. The aim of this research is to evaluate existing masonry block shapes filled with different thermal insulation using conjugated heat and moisture transport finite element simulations with material properties measured in laboratory. The research compared four different internal structures: trapezoidal, triangular, rectangular, and with mixed shaped gaps according to existing masonry blocks. In the gaps, different thermal insulations were considered, such as mineral wool, expanded perlite and polyurethane foam. The research demonstrated that the perlite as filling material does not have a great effect on thermal conductivity comparing to unfilled blocks; however, polyurethane foam with an optimal internal structure can improve the thermal performance. Manufacturing inaccuracies in the materials’ hygrothermal properties influences their performance, since a little difference in thermal conductivity has a noticeable impact on thermal transmittance, and it may result in underperformance according to regulations.