text: The thermal conductivity is a measure of the capacity of a material to conduct heat. In a nanofluid this conductivity is influenced by the nanoparticles suspended in the solution. A simple model only considered the thermal conductivity of the liquid and the suspended solids. This is called the Maxwell–Garnett model (1891) and is defined as:
  In which , ,  are respectively the effective thermal conductivity, the thermal conductivity of the fluid and the thermal conductivity of particle and  is the packing fraction of the particles. This model is not very accurate for nanoparticles for it does not take into account the interfacial layer formed by the fluid around a nanoparticle.
  In 2006 K. C. Leong et al proposed a new model, one which took into account the existence of an interfacial layer. They did so by considering the area around a nanoparticle and stating it exists of three separate regions. Each of them with a specific but different thermal conductivity. This resulted in the following model:
  In which  is the effective thermal conductivity, ,  and  the thermal conductivity of respectively the particle, the fluid and the interfacial layer.  is the packing fraction of the fluid or . And  and , with  or the ratio of the thickness of the interfacial layer to the particle size. This model was shown to be more in agreement with the experimental results, but is limited in its applicability for there is not yet a theoretical way to establish the thermal conductivity, or the thickness of this layer.