Abstract: Vermiculite exfoliation is based on the principle when water between the layers evaporate, and the crystal layers spread out pressured by the steam. As a result, elongated, curved particles are formed. The thermal properties of the final product formed are directly related to this exfoliation amount. In this experimental work, exfoliation characteristic of natural vermiculate is studied. A series of experimental analyzes were carried out to examine the expandability of natural vermiculite at different heating temperatures by the Na+ modification method. In addition, the expansion ratios of Na+-modified and unmodified vermiculite samples were analyzed comparatively. Each of the raw and Na+ modified vermiculite material groups prepared for the thermal expansion process was experimentally performed by recording the exfoliation states and times at six different heating temperature values of 350 oC, 450 oC, 530 oC, 620 oC, 710 oC and 840 oC, respectively, in a laboratory environment. In the second phase of the study, thermal properties of new generation composite mortars produced with exfoliated vermiculite aggregate were experimentally analyzed. Parameters such as thermal conductivity, heat storage capacity, specific heat and heat dissipation coefficient of mortar test samples prepared with exfoliated vermiculite aggregates are analyzed and discussed here. Test results showed that Na+-modified vermiculite samples expanded better than unmodified vermiculite samples for all expansion temperatures. When Na+-modified expanded vermiculite is evaluated in composite mortars, it also reduces the unit weight of the mortar as it expands more and the unit weight of itself decreases. Accordingly, the compressive strength of the mortar decreases relatively. However, it has been determined that the thermal comfort properties of mortars using Na-modified exfoliated vermiculite are better than the thermal comfort properties of composite mortars produced using unmodified exfoliated vermiculite.