Which Way Should Polycarbonate Sheets Face? (UV Side Explained)

Which Way Should Polycarbonate Sheets Face? (UV Side Explained)

Correct orientation is one of the most important aspects of installing multiwall polycarbonate roofing. A frequent question from DIY users and even professional installers is:

“Which side of a polycarbonate sheet should face outwards?”

This guide explains how to identify the UV-protected side, why orientation matters, and how to avoid common installation errors.

Why Polycarbonate Sheets Have a UV-Protected Side

Most multiwall polycarbonate sheets are manufactured with a UV-protective layer on one face. This layer is designed to help the sheet cope with outdoor exposure and sunlight.

The UV-protected side is intended to face outwards, towards the sun.

How to Identify the UV-Protected Side

Manufacturers mark the UV side clearly to prevent confusion.

1. Printed Protective Film

The UV-protected face typically has printed film, which may show:

  • Brand markings

  • Installation instructions

  • Directional arrows

  • Notes such as “UV protected side” or “This side up”

The reverse side usually has clear or unprinted film.

2. Labels or Stickers

Some sheets include small labels or arrows to indicate the correct orientation.

3. Product Documentation

Packaging or technical sheets may specify the UV-facing surface for each product type.

Always check these indicators before removing any protective film.

What Happens If Sheets Are Installed the Wrong Way Around?

Installing sheets with the UV side facing inward can affect how the material responds to sunlight. Potential issues may include:

  • Discolouration over time

  • Reduced resistance to outdoor exposure

  • Surface degradation

Correct orientation helps the sheet perform as intended in outdoor conditions.

Does the UV Side Affect Light or Heat?

The UV-protected face works together with the sheet’s finish — such as clear, opal, bronze, or reflective coatings — to manage:

  • Brightness

  • Glare

  • Light diffusion

  • Solar gain

To choose the right finish for your application, you can compare options here:
👉 https://polycarbonatex.co.uk/blogs/news/clear-vs-opal-vs-bronze-polycarbonate-sheets-explained

Do All Polycarbonate Sheets Have a UV Side?

Most multiwall sheets designed for roofing in the UK include UV protection on one surface. However:

  • It is always best to confirm with the product information

  • Do not assume both sides are treated

  • Follow any markings on the protective film carefully

Browse available sheet types and thicknesses:
👉 https://polycarbonatex.co.uk/collections/multiwall-polycarbonate-sheets

When Should the Protective Film Be Removed?

Best practice during installation is to:

  1. Keep the protective film on the sheet

  2. Fit and secure the panels

  3. Remove the film once the installation is complete

This helps prevent scratching and ensures orientation can still be checked during fitting.

Installation Tips to Avoid Mistakes

  • Check the printed protective film before cutting or installing

  • Stack sheets in the same orientation to avoid confusion

  • Keep film on during fitting

  • Use glazing bars and fixings that match the sheet thickness

  • Install with suitable tape and end closures on open flutes

Accessories for correct installation:
👉 https://polycarbonatex.co.uk/collections/multiwall-accessories

Frequently Asked Questions

How do I know which side is UV protected?

Look for printed film, labels, or markings indicating “UV protected side” or similar wording.

Should the UV side face up or down?

It should always face outwards, toward the sun.

Does orienting the sheet incorrectly matter?

Yes. Correct orientation helps ensure the sheet functions as intended in outdoor conditions.

Are both sides UV protected?

Usually not. Most multiwall sheets have UV protection on one face only.

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