Nowadays, 3-D printing technology is very often applied in industry due to design cycles shortening and surface quality improvement when comparing to conventional manufacturing technologies. In order to adapt 3-D printed materials as thermal barriers, it is necessary to determine its thermophysical properties. As far as thermal insulation is concerned, the lowest thermal conductivity is required and therefore the crucial parameter of the material is the porosity. This paper presents the results of experimental investigation of effective thermal conductivity of thermal barriers with variable porosity fabricated by the fused filament fabrication technology. Also the numerical study was presented. The commercial code - COMSOL multiphysics was used to model the coupled heat transfer. The model was than validated by comparing the numerical and experimental results. For each sample the density and thermal conductivity were determined experimentally. The influence of the size and shape of the cell on the formation of free convection was investigated in particular. The effect of the conduction and radiation on temperature and velocity profiles within the enclosure has been analyzed. In addition, the dominant heat transfer mechanisms as a function of density have been identified.