The structural element in the Thermacell system is the concrete in-fill in the polystyrene blocks. The blocks themselves - and any finishes and cladding - are non-structural. Tests carried out by the James Cook University in 1994 and the University of Newcastle in 1991 showed that the behaviour of the reinforced concrete filling system is similar to normal reinforced concrete. Consequently AS.3600 'Concrete Structures' can be applied to the design of Thermacell buildings. AS.3700 and SAA.3700 Masonry Code can also be referred to for guidance, as it specifically addresses the construction of reinforced concrete cores. These blocks can be used in heavy cyclonic areas as well.

To demonstrate the strength of the concrete core of our various block sizes, we stripped away the foam blockwork to show the concrete core (shown below). In actual practice, the polystyrene blockwork is never stripped away, as the polystyrene blockwork encases the concrete core insulating it from heat and cold exchanges, thereby preventing expansion and contraction in the walls. That is why we do not need expansion joints in any of our walls or buildings.