Pillow plate is a metal heat exchanger formed by inflating.
Pillow plates are generally made of two spaced thin steel sheets, (laser) welded to each other. The space between the plates is pressurized to deform one or both plates in order to provide a space in which a heating (or a cooling) medium can circulate. Creating the single or double embossed plates.
Pillow plate can be produced with different metals. Appearance in industry is Stainless steel 80%, Normal steel 10%, Aluminium and Titanium 5% other materials 5%.
Herman Oonk, with his company OMEGA Thermo Products, invented the laser welded machines to weld plates together with a spot pattern. He named the welded plates, Pillow Plates. Because Oonk was a pure technician, without any interest in marketing, he never registered the name Pillow Plate. Other companies also began to manufacture Pillow Plates and used the name. Nowadays pillowplate or pillow plate is a general term.
The German company LOB GmbH  from Cologne has been using Pillow plates, also known as the WTP-System®, for more than 20 years now for vessel heating systems and as plate heat exchangers. LOB's WTP-heating system serves as an alternative to the half-tube coil and double-walled jacket. It can be used at excess operating pressures of up to 50 bar and temperatures of 300° Celsius or more. Plate heat exchangers are designed for condensers, evaporators, cooling traps, gas-gas and liquid-liquid applications.