Gallina Polisoft® Light Diffusing Twin Wall Sheet, 8mm

8mm twin wall polycarbonate sheet, nominally 5/16" thick, built as 2 skins separated by continuous webs. It carries 80 percent light transmission and a U-value of 3.3 W/m2K per EN ISO 10077-2.

The hollow section is what the product is for: at 0.307 lb per square foot it weighs about a sixth of what the same thickness of solid sheet would, and the trapped air does the insulating work that a solid panel of this thickness cannot.

Impact strength runs about 200 times that of glass and 10 times that of acrylic, and the panel is warranted against hail breakage - tested against 20mm spheres at 21 m/s, which is a 20mm hailstone at about 47 mph. The diffusing surface scatters direct sun into even light, which is why this grade goes into greenhouses.

It cold-bends along the flutes to a minimum radius of 51", dry, with no heat.

Polycarbonate moves about 0.065 mm per metre per degree C, which works out to roughly 1/8" of growth in every 4 feet of panel across a normal year. Every fixing hole is drilled 1/16" larger than the screw, the screws are set with neoprene or EPDM backed washers and left just snug, and the panel edge is never bedded in adhesive or putty. Dark panels need close to twice the allowance of clear, because they run hotter in the sun.