When constructing a gas delivery system for GC, choosing the proper tubing material is very important and will help to eliminate future problems and improve the overall quality of the gas system. Although there are many common tubing materials available, some pose safety or cleanliness problems. Non-metallic types of tubing such as polyethylene and PTFE are not recommended for GC applications due to their permeability and difficulty in cleaning. This type of tubing can be used for non-critical applications, such as pressurizing pneumatic lines, however, be aware of its pressure limitations. In view of these problems, the list of appropriate tubing materials has been narrowed down to two: copper and stainless steel.