This lecture covers the analysis of conductive heat transfer in non-steady-state conditions, focusing on the short-term response in homogeneous and isotropic media. The lecture discusses the thermal diffusivity, the reduced temperature equation, the error function, and characteristic quantities in materials like copper and wood. It also explores the diffusion delays, the depth of diffusion, and the periodic regime in a half-space. The solution of the heat equation, the diffusion phenomenon, and the attenuation of the propagation are analyzed, along with the depth of penetration. The lecture concludes by summarizing the key concepts discussed.