Reactor vessel is a broad-based statement that can be very interpretive. The typically accepted reactor will contain some type of material that will undergo a controlled chemical and/or physical change while contained within the vessel. These changes can be for products that are intermediates or they can be for final consumer use. The usual designs can range from a simple closed container to a vacuum-jacketed ASME type vessel. Jackets for the vessel can be constructed from half-pipe, half-oval, or conventional. The most common choices of materials are stainless steel followed by carbon steel. The lesser used materials are typically materials selected for their resistance to the specific material that will be contained within the vessel. The internal finish of the reactor vessel is also selected based on the vessels end use. Some food and pharmaceutical applications may require an electro-polished interior, while some less stringent applications for polymers and intermediates may only require a smooth non porous finish which can and does reduce the overall cost of the reactor vessel.