The culprit behind the yellowing and brittleness of PC boards is ultraviolet (UV) radiation. Although PC itself is extremely tough, it undergoes photo-oxidative degradation under prolonged exposure to sunlight, leading to the breakage of its molecular chains.

The Invisible Protective Layer
To address this issue, manufacturers apply a high-concentration UV co-extruded coating to the surface of the board. This film, only about 50 micrometers thick, acts like sunscreen, blocking 99% of UV rays. The key point is that most PC boards are only protected on one side. If you install the board with the side without the UV layer facing the sun, the board will rapidly age and become brittle within one or two years, even breaking easily like a biscuit.

Identifying the Pitfall
The only way to distinguish the front and back is through the text on the protective film. Usually, the film printed with product instructions, installation guidelines, and the words “This side faces out/UP” corresponds to the side with the UV layer. If you peel off both protective films, it’s almost impossible to tell with the naked eye which side is the “sun-protected side.”

Implementation Recommendation
Before installation, always ensure that the side with the text faces the sun. If you accidentally peel off the protective film, you can try the water droplet test: the surface tension of the side with the UV layer is usually slightly higher, so the water droplet will be more rounded. However, the safest method is to make a mark with a marker before peeling off the film.

**If you would like to know the advantages of polycarbonate sheets, please kindly check the post [What are advantages of polycarbonate sheets?]