The present work aims to investigate the thermal properties of the Lebanese metakaolin-based geopolymer produced with two different types of alkali activators.  An experimental approach was done to assess the thermal properties. First, a laboratory characterization of the Lebanese Geopolymers was performed. It was secondly followed by the production of different geopolymeric mortars with two sets of alkali activators (Na or K-based).  The thermal conductivity was then measured by the use of hot disk apparatus. As such, the influence of the use of various liquid activators was analyzed by linking the attained physical, chemical, and microstructural characterization with the thermal and mechanical results. The obtained results highlighted the influence of the alkali-(Na or K)OH activators on the properties of the various geopolymeric mortars. A correlation was noticed between the pores assessed from the microstructural analysis and its impact on thermal conductivity. Thereby emphasizing the role that certain parameters play on the insulating properties of the manufactured mortars, such as composition and pores.