What is a major reason PEX should not be used outdoors?

• A. Ultraviolet rays cause PEX to break down quickly.
• B. It cannot handle high water pressure.
• C. It is susceptible to rust from metals.
• D. It expands when exposed to sunlight.

Answer: (A)

Ultraviolet radiation from the sun is the main reason PEX shouldn’t be used outdoors without protection. PEX tubing is a plastic that handles chemicals and pressure well, but its polymer chains break down when exposed to UV light, making the material brittle and prone to cracking over time. This degradation can lead to leaks, especially under outdoor temperature changes and pressure fluctuations. That’s why outdoor installations are avoided unless the pipe is buried, shielded in UV-stabilized conduit, or a UV-resistant variant is specifically rated for exterior use. The other options aren’t the primary limitation: PEX can handle relatively high pressures when properly rated, rust isn’t a concern since it’s plastic, and expansion is primarily due to temperature, not sunlight.