Which type of material is NOT commonly used for making pipes?

Fiberglass is not commonly used for making pipes in public works applications when compared to the other materials listed. While fiberglass piping is certainly available and has specific uses, especially in industries that require resistance to corrosive substances, its application is not as widespread in municipal water and sewer systems as cast iron, plastic (PVC), and ductile iron.

Cast iron has been a traditional and durable choice for many years, particularly for gravity sewer applications. Plastic pipe, specifically PVC, is extremely popular due to its lightweight, corrosion resistance, and easy installation. Ductile iron is favored for its strength and flexibility, making it suitable for various utilities and heavy service environments.

In summary, while fiberglass has its merits in niche applications, it does not hold the same level of common usage in the context of typical municipal pipe material selections as the others listed.