Diffusivity quantifies how readily a substance diffuses through a medium, expressed as a diffusion coefficient with units of area per time. Thermal diffusivity describes the analogous spread of heat through a material, governing heating and cooling rates in thermal processing. Food engineers use moisture diffusivity to model drying curves and thermal diffusivity to predict temperature profiles during pasteurization and freezing, making it a core property in process design and equipment sizing. Reliable diffusivity data therefore shorten development time for new drying, freezing and heating processes.