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Real building's and their components experience dynamic thermal transmission. It is possible to represent thermal transmission as either a supposition of local constitutive convolution equations in a local region of the solid or as a directed graph network between connected thermodynamic regions within the solid. Both the loacl constitutive convolution and directed graph network representations are based on response factors which can, in principle, be used to estimate dynamic thermal transmission of the building components. The response factors can also be used to predict the performance of the materials under a range of design loadings. These response factors for each representation can be estimated directly from time series data of the physical observables under general stochastic boundary conditions. Indeed, it can be demonstrated that each of the representations can accurately characterise the thermal performance of building components. The purpose of this paper is to show that only the load constitutive equations yield, for all cases considered, the correct values for the physical properties of the materials under test, whereas the directed graph network representations are unreliable. This is because directed graph network representations are ill posed for the one dimensional flow case and are likely to lead to erroneous predictions for the design performance of buildings. The load constitutive equations allow the measurement of thermal conductivity and transmission of building components in the field. Thus providing a unique insight into the actual thermal performance of constructions in use.