Which of the following materials is considered semi-rigid?

Type L copper tubing is classified as semi-rigid due to its flexibility and structural integrity, which allows it to be bent for installations without the need for fittings in many cases. This characteristic makes it suitable for a variety of plumbing applications, providing a balance between being easily handled and installed while still maintaining strength to resist pressure and corrosion.

Type M and Type K copper pipes differ in their wall thickness and flexibility. Type M has thinner walls, making it more flexible but less robust, while Type K, having the thickest walls, is regarded as more rigid. The semi-rigid classification of Type L lies in its ability to withstand some bending without risking damage, making it ideal for tight spaces and complex layouts in plumbing systems where some movement is necessary.