Twinwall Polycarbonate

Our twinwall range runs from 4mm to 10mm. The 4mm and 6mm sheets are clear and mainly used for greenhouses, where 4mm passes about 82% of daylight. The 10mm sheet comes in clear, bronze and white opal and suits small canopies, porches and shed roofs. All are cut to size, and we stock the matching tapes for 10mm.

The ribs between the two skins act like a row of small beams, so the sheet is stiff along the channels and weaker across them. It needs support at its edges, which is why we recommend a maximum width of 700mm for 10mm twinwall. Run the flutes down the slope so condensation drains out. Thicker multiwall sheets have more ribs and span further.

One side only. The UV-protected face is marked by the printed protective film and must face the sun. Fitted the wrong way up, we have seen twinwall yellow and crack within a couple of years. Fitted correctly, the sheet is warranted for ten years against loss of light transmission. Keep the film on until the sheet is in position.

10mm twinwall comes in clear, bronze and white opal. The 4mm and 6mm sheets are clear only, because they are made for greenhouses where plants need the most light. Clear 10mm passes about 79% of daylight, bronze about 35% and opal about 30%. Bronze cuts glare on a sunny aspect, while opal gives a soft, even light.

Triplewall insulates better. Our 16mm three-wall sheet loses about a fifth less heat than 10mm twinwall, because the extra skin adds a second layer of trapped air. Twinwall is lighter and lets in a little more light, so it suits greenhouses and simple covers. Choose 16mm or thicker for anywhere you want to sit in comfort.