Multiwall Polycarbonate Sheet
Polycarbonate Sheet
Light without the heat
Multiwall polycarbonate has two or more walls with air channels running between them. The trapped air gives it far better insulation than a single skin, which is the point: it admits daylight without bringing in the solar heat that usually accompanies it.
It is also sold as multilayer sheet, and in coloured form as coloured polycarbonate sheet. Solid or compact polycarbonate is the single skin version, chosen where optical clarity matters more than insulation.
Where the extra cost is justified
Anywhere the building is conditioned, or where people work directly under the roof light for long periods. A single skin roof light over a workstation in summer is uncomfortable; a multiwall one over the same spot is markedly better.
It also suits canopies, walkways, skylights and atria, where the sheet is close to the occupants and both glare and heat are noticeable.
Channel direction and drainage
The channels must run down the slope, not across it. Run across, they trap condensation and dust with nowhere to drain, and the sheet develops a permanent streaked appearance from inside that cannot be cleaned out.
Open channel ends should be closed with the correct tape: a breather tape at the bottom that lets moisture out while keeping insects and dirt from getting in, and a sealed tape at the top. Ordinary adhesive tape at both ends traps moisture inside the channels, and that is what causes the cloudy look people blame on the sheet.
UV face and thermal movement
As with any polycarbonate, the UV protected face goes outward, and the sheet expands and contracts with temperature far more than the metal it is fixed to. Fixing holes are oversized and fasteners set firm rather than crushed.
Multiwall is also more prone to showing over-tightening than a profiled single skin, because crushing the walls at a fixing point destroys the structure that makes it stiff.
What to send us for a quote
The area, the span between supports, whether it is roof, canopy or skylight, and the sheet thickness or wall count if the specification names one. Tell us whether the priority is insulation or clarity, because that decides multiwall against solid.
Frequently asked questions
What is the difference between multiwall and solid polycarbonate?
Multiwall has air channels between walls, which insulates much better but diffuses the view. Solid is a single clear skin with better optical clarity and much less insulation.
Why do the channels look cloudy from inside?
Moisture trapped in the channels, usually because the ends were sealed with ordinary tape or the channels were run across the slope instead of down it.
Which way should the channels run?
Down the slope, so any condensation can drain out at the bottom edge.
Is it stronger than a single skin sheet?
For its weight it is stiffer, because the walls and channels form a structural section. It still must not be walked on.
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