Process Engineers And Associates manufactures and Supplier of Pillow Plate Heat Exchanger as per the set standards of the industry. Pillow-plate heat exchangers are composed of parallel plates arranged as a stack. In this way, inner channels within the pillow-plates alternate with outer channels between the adjacent plates, and thus, a structure with alternating inner and outer channels is arranged for the heat transfer media. This chapter deals with fundamentals of PPHE covering manufacturing, basic design considerations and general application fields. The geometric variability of PPHE is extremely high, while their performance strongly depends on the particular geometric details. Therefore, the relevant parameters characterizing the complex pillow-plate geometry as well as the corresponding methods for their calculation are considered. These parameters include the internal and external heat transfer surface areas, cross-sectional areas and characteristic lengths. Furthermore, the welding spot arrangement is discussed, which is important for the flow pattern and overall thermo-hydraulic performance characteristics.