35mm Multiwall Polycarbonate

A clear 35mm sheet passes about 63% of daylight, roughly two thirds of what falls on it, and about the same as 32mm. The seven-wall structure that gives 35mm its insulation also scatters some light, so the room feels bright but soft rather than glassy. Choose bronze, opal or heat guard instead if glare or summer heat is the concern.

Yes. 35mm is the thickest multiwall sheet we stock and the current standard for new conservatory roofs. It loses about a sixth less heat than 25mm, and only a little less than 32mm. It comes in clear, bronze, white opal, bronze/opal dual colour and opal heat guard, in sheets up to 2100mm by 7000mm, cut to size.

We recommend a maximum sheet width of 1000mm for 35mm multiwall without extra support. The manufacturer allows wider spans at light loads, but 1000mm is the safe figure for a DIY roof. That figure is about the sheet, not the rafters beneath it, so check your wind and snow exposure, or call the technical team before ordering.

Only slightly. 35mm loses a little less heat than 32mm, but the difference is small and you are unlikely to notice it in a heated room. Both are seven-wall box structures passing about 63% of light in clear, and both insulate better than 25mm. Choose 35mm for a new roof and 32mm to match panels in an existing roof.

The largest 35mm sheet is 2100mm wide by 7000mm long. We cut to your width and length from that, to a tolerance of plus or minus 5mm. Bear in mind the recommended maximum width of 1000mm without extra support. Cut sheets are bespoke and non-returnable, so measure carefully. We can pre-tape the ends on request.

What are pre-taped edges on multiwall polycarbonate sheets?

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?