Multiwall Polycarbonate

A multiwall sheet traps still air between its skins, and still air is a poor conductor of heat. A solid sheet has no air layer, so heat passes straight through it. Each extra wall adds another air layer: 16mm loses about a fifth less heat than 10mm, and 25mm about a third less than 16mm. More walls also mean less light.

For a lean-to, canopy or covered walkway, 16mm is the usual choice. For a conservatory you heat and sit in through the winter, choose 25mm or thicker, with 35mm the current standard for new roofs and the best insulator. If you are replacing panels in an existing conservatory, match the thickness already fitted, which is often 32mm.

One side only, on every multiwall sheet we sell. The UV layer is co-extruded into the sheet during manufacture, and the printed protective film marks that face. It must face the sun. Fitted the wrong way, the sheet yellows and cracks within a couple of years. Fitted correctly, it is warranted for ten years against loss of light transmission.

We give a recommended maximum width for each thickness: 10mm 700mm, 16mm 800mm, 25mm 900mm, 32mm and 35mm 1000mm. Thicker sheets are stiffer, so they span further. The manufacturer's tables allow more at light loads and less under heavy snow, so our figures are the safe DIY numbers. Check your wind and snow exposure, or call the technical team.

Yes, with limits. Multiwall sheets are made for roofing and glazing, and that is what we sell them for, but they also work as lightweight partitions or screens in outbuildings, workshops and garden rooms where you want daylight without a clear view through. Opal suits that best. For a habitable room, check fire and Building Regulations requirements before fitting one.

Pre-taped edges mean that protective tapes have already been applied to the open ends of your multiwall polycarbonate sheets before delivery, saving you time during installation.

At The Polycarbonate Store, our complimentary pre-taping service is available on 10mm, 16mm, 25mm, 32mm and 35mm twinwall and multiwall polycarbonate sheets.

The two open ends of the sheet's hollow channels (flutes) are taped differently:

• Top edge – Aluminium sealing tape: Solid silver tape seals the upper end of the flutes, helping prevent water, dirt and debris from entering.
• Bottom edge – Anti-dust breather tape: Helps prevent dust and insects from entering while allowing ventilation and moisture to escape, reducing the risk of condensation build-up.

For a standard sloping roof, the aluminium-taped edge must be positioned at the top, with the breather-taped edge at the bottom, towards the gutter. The tapes should remain in place during installation.

Important: Pre-taping only covers the two open flute ends, not all four sides of the sheet. It does not replace the need for PVC sheet end closures, which should be fitted over the taped edges to provide additional protection and a neat finish. Pre-taping also does not completely prevent condensation.

During preparation, approximately 10mm of protective film is removed from each taped end. This may leave a visible preparation line, which is normally concealed by the roofing accessories. If you need to trim a pre-taped sheet, the newly exposed flutes must be cleaned and re-taped correctly before installation.

For curved roofing or other applications, the required tape arrangement may differ. Please contact us before ordering if you are unsure.

For further information, read our full guide: What Do Pre-Taped Edges Mean on Multiwall Polycarbonate Sheets?