It is made from natural or synthetic rubber and is usually tear resistant, durable and supple. In order to be shaped and bent in different ways, the tubing is soft and can be twisted, tied and stretched without cracking or becoming kinked. The walls of the tube are strong enough to support themselves while being thin enough to allow the maximum amount of fluid to pass through unrestricted.
Some materials used in rubber tubing are more flexible than others. Gum rubber is made from pure gum and is a natural rubber that exhibits high flexibility under stress. Latex tubing is also a natural substance that is flexible. High performance tubes made out of Viton or EPDM (ethylene propylene diene monomers) are flexible to some degree but are more valued for their resiliency, durability and industrial applications. Because flow lines cannot always be designed in straight lines or direct paths, flexible rubber tubing is invaluable for delivering liquids and gases to places that are difficult to access or that are very small. For example, intravenous lines use flexible tubing to make the patient more comfortable; if a stiff tube was used, the patient would need to remain still and would have a small range of motion.
Natural rubber is made from latex, a milky substance found in the bark of certain trees. When the bark is cut, latex drips out and can be collected. At the processing plant it is mixed with water and chemicals, which thicken it and add certain qualities such as color or buoyancy, as in the cases of black rubber tubing and neoprene tubing. Natural rubber is made up of isoprene monomers while synthetic rubber can be made up of many different kinds of molecules. After the rubber has been mixed it is given its shape. For rubber tubes, there are three main ways this is done: molding, extrusion and dipping.
Liquid rubber can be poured in a mold and pressed into place; for tubes, this is done in halves that are later attached. Rubber extrusion involves forcing raw rubber material through an extrusion die. The third method is used most frequently for latex tubing. A cylinder of the desired diameter is dipped into the rubber mixture and slid off when dry. After any of these processes, the rubber is dried and cured. Some tubing undergoes vulcanization, which is the process applying heat and sulfur to a rubber in order to improve its qualities of strength and durability.