Same plastic. Different shape. If you are covering an area and want daylight without heat loss, use twin wall. If you need to see through it clearly, or the panel gets hit, use solid. Everything below is why.
Both of these are polycarbonate. Same resin, same UV behavior, same chemistry, same expansion rate. Nobody is arguing about which polymer is better, and any comparison that tells you one “outperforms” the other has skipped the actual question.
What differs is the cross-section. Twin wall is two thin skins held apart by ribs, with sealed air cells between them. That trapped air is the entire product — it is where the insulation comes from, why the panel is so light, and why it spans further than its weight suggests. It is also why you cannot see through it clearly, and why you cannot cut a machine guard out of it.
Solid sheet is exactly what it sounds like. Optically clear, takes impact anywhere on the panel, cuts and machines like a sheet of plastic. And it insulates about as well as a pane of glass, which is to say barely.
Twin wall figures are Gallina’s published weights. The two solid figures are calculated from the published specific gravity of 1.2 (ASTM D 792) rather than manufacturer-published — it is only arithmetic, but it is our arithmetic, so it is labeled that way.
Solid sheet passes light you can see through. Twin wall passes light it has already scattered — daylight without glare or hot spots, but no view. Do not read these four numbers as four versions of the same thing.
A single sheet of solid polycarbonate is single glazing. Nobody publishes a U-value for it as a standalone panel, so we are not going to print one — the honest statement is that it insulates about as well as one pane of anything. Twin wall is roughly 70% better, and the reason is the sealed air cell rather than anything about the plastic. If insulation is why you are on this page, that is the whole answer.
| Property | Twin wall | Solid sheet |
|---|---|---|
| Structure | Two skins, ribs, sealed air cells | Solid through the section |
| See through it | Translucent — diffused, no view | Clear — 88% and a true view |
| Insulation | U-0.61 at 6mm, U-0.58 at 8mm | Single glazing, negligible |
| Weight per ft² | 0.27–0.31 lb | 0.78 lb at 1/8″, 1.56 lb at 1/4″ |
| Impact | Strong for its weight; the skins are thin | 800 in·lbs at 0.125″, ASTM D 3763 |
| Cut to size | Yes — flutes must run with the slope | Yes, any direction |
| Machined, routed, drilled | Limited — you are cutting a hollow panel | Yes |
| Cold bending | 39″ min radius at 6mm, 59″ at 8mm | Yes, radius depends on gauge |
| Thermal expansion | 0.065 mm/m/°C | 0.000038 in/in/°F |
| UV protection | Coextruded on the exterior face | UV-resistant grade (IS SG) |
| Warranty | 10 year | 10 year limited (IS SG) |
| Stocked in Sparks | 6mm and 8mm clear, 48×96 and 48×120 | 1/16″ through 1/2″, clear plus tints |
| Cost per ft² covered | Lower | Higher |
Twin wall figures are Gallina’s published data. Solid figures are Calsak’s published typical properties for PolyGuard, rev. 02/10/2016, reproduced as published. The two expansion figures look different because the manufacturers publish in different units — converted, they are effectively the same number, which is what you would expect from the same polymer. Both need the same clearance allowance. Typical properties, not specifications.
An 8mm twin wall panel weighs about a fifth of what a 5/16″ solid sheet of the same footprint weighs, because most of the section is air. That air buys the insulation, most of the stiffness relative to weight, and a much lower cost for the area covered.
What it costs you is everything that depends on the material being continuous: optical clarity, impact strength at any point on the panel, and the ability to machine it into a part. Those are not weaknesses in twin wall. They are what you traded away, on purpose, to cover a roof for a fraction of the weight and cost.
The mistake is almost never picking the wrong one for a roof. It is trying to use twin wall for something that wanted a solid panel — a guard, a window, a machined cover — because the price per square foot looked better.
Tell us what you are covering, what the frame is, and whether anyone needs to see through it — and we will tell you which one to use, including when the answer is neither. We stock both in Sparks: twin wall by the pallet in 6mm and 8mm with H and U profiles on the shelf, solid sheet from 1/16″ through 1/2″ in clear and tints. If it is a roof or a canopy, send us your span, purlin spacing and design load and we will pull the manufacturer’s load chart for your configuration before you buy framing. Call (775) 358-8211 or send us the details.
As a material, no — it is the same polymer. As a panel, it depends entirely on what you are asking of it. Twin wall is remarkably stiff for its weight and spans well between purlins, which is why it roofs things. But the skins are thin, so a concentrated impact in one spot goes through it far more easily than it goes through solid sheet. For a canopy that takes hail, that is fine. For a machine guard that takes a thrown part, it is not.
Not clearly, and you should plan on that. It passes 80–81% of visible light but scatters it through the flutes, so you get bright, even, diffused daylight rather than a view. That is a feature for a greenhouse or a shop skylight and a problem for a window. If someone has to look through it, use solid.
For covering area, twin wall, and not by a small margin — you are paying for far less material per square foot. For a small part, solid usually wins once you account for the tape, the U-profile, and the labor to seal the flute ends. The crossover depends on the job, so tell us the size and we will price both.
Cut, yes — we cut it to size the same day, with the flutes oriented for your slope. Drilling is different: fastener holes go through both skins and must be oversized for expansion, and you cannot machine a shaped part out of it the way you can with solid. Anything routed, engraved, thermoformed, or line-bent to a profile needs solid sheet.
Yes, and it matters on both. Twin wall carries a coextruded UV layer on the exterior face; PolyGuard IS SG is a UV-resistant grade with a protected side. The masking film tells you which face it is. Install either one backwards and it yellows early, and neither warranty covers it.
Both, in Sparks. Twin wall we buy by the truckload and carry in pallet quantities in 6mm and 8mm clear, 48×96 and 48×120, with H and U profiles stocked for both thicknesses — there is no pallet minimum, one sheet is fine. Solid sheet runs 1/16″ through 1/2″ on the rack in clear, with gray, bronze and black in the common gauges, and we source to 2″. Both cut to size same day.
Full twin wall specs and stock → · Full solid polycarbonate specs and stock → · Acrylic vs polycarbonate →
Whatever you need — one piece or one hundred, a quick cut or a full fabrication run — we're here. Serving Northern Nevada since 1979.