Which of the following is NOT a common material used in pneumatic tubing?

Steel is not a common material used in pneumatic tubing due to its weight and lack of flexibility compared to other materials. Pneumatic systems often require tubing that is lightweight and flexible to facilitate easy routing and installation within confined spaces.

Polyamide, polyurethane, and PVC are all popular choices for pneumatic tubing. Polyamide is known for its excellent strength, chemical resistance, and durability, making it suitable for various pneumatic applications. Polyurethane tubing is appreciated for its flexibility and ability to withstand repeated bending and flexing, making it ideal for applications where movement is a factor. PVC is often chosen for its chemical resistance and affordability, commonly used in less demanding applications.

In contrast, steel does not offer the same level of flexibility or the lightweight characteristics necessary for most pneumatic tubing applications. Therefore, it stands out as the least suitable option in this context.