This lecture covers the concept of the flux equation in the context of sorption and transport in cementitious materials, explaining the relationship between heat or moisture flux, thermal conductivity, and temperature gradient. It also delves into examples and applications of the flux equation, including Fick's first law. Additionally, it discusses water content and related variables such as water saturation, reduced water content, and capillary potential, providing insights into transport parameters and diffusivity. The lecture concludes by summarizing the key points covered.