The contribution is focused on investigating the heat transfer via natural convection which originated as an effect of changed air density by heating the horizontal sample in the area given. For this research we used samples of a new material made in the Russian Federation -the foam concrete which was reinforced by PET fibres. The samples were heated by an electric heating device from the bottom. The temperature fields originating above the horizontal sample surface were visualised by means of the holographic interferometric contactless method in real time. The holographic interferograms of the temperature field were analysed, and then the local heat transfer parameters were calculated: the heat transfer coefficient α, and the heat conductivity coefficient λ.