Abstract : Electronic engineers for some time have been depending on the principle of regeneration, known better as 'thermal inertia,' for maintaining components of equipment packages at reliable levels during supersonic flight. Generally for certain aircraft systems, it was recognized that no cooling or an inadequate amount of refrigerated cooling air would be supplied to the electronic equipment during supersonic flight. The heat capacity of the mass of the electronic equipment had to be depended upon to absorb heat from electronic components for a given period of time. The discussion presented provides theory and mathematical equations for calculating temperatures for cooling and heating packed bed regenerators.