If you are comparing an insulated sectional door for a warehouse, cold store, factory or loading dock, the first question is usually simple: what is the panel actually made of? Skin material, foam density, panel thickness and seals all decide how much energy you save and how long the door lasts. This guide explains each layer in plain technical terms, using the specification of the Cutedoor QT-1 Insulated Sectional Door as a real example.
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Almost every modern insulated panel is a sandwich structure: two thin metal skins bonded to a foam core. The skins handle impact, weather and appearance; the core handles heat flow and stiffness.
Galvanized steel is the most common skin. A zinc coating protects the base steel from corrosion, and the metal gives good dent resistance for forklift-heavy sites. On the QT-1, the steel skin is 0.4 mm or 0.5 mm zinc-galvanized plate, and the surface finish can be chosen to match the building design.
Aluminum is lighter and naturally resists rust, so it suits humid, coastal or washdown environments. The QT-1 aluminum option uses a 0.6 mm plate. The trade-off is that aluminum is softer than steel, so choose it where corrosion matters more than impact.
“Double-skin” means both faces of the panel are metal, with foam between them. Because the inner skin is also metal, the panel is easy to clean and hygienic, which is why this design is widely used in food, pharmaceutical and logistics buildings. Each QT-1 panel is 500 mm high, and sections are joined with galvanized screwed hinges at the sides and center.
The standard core is polyurethane foam, injected between the skins and expanded so it bonds to the metal. This adhesion makes the panel behave as one rigid composite instead of two loose sheets. Cutedoor produces panels on a fully automated continuous production line, which helps keep foam density and thickness consistent from panel to panel.
The QT-1 uses environmentally friendly polyurethane foam at a density of 48 kg/m³. Density is a balancing act: too low and the panel feels soft and loses stiffness; too high and the door becomes heavier and costs more without a proportional insulation gain. Around this range is widely regarded as a practical balance of strength, weight and thermal performance for sectional doors.
Heat moves through a solid by conduction, and through air by convection. Closed-cell PU foam traps a low-conductivity gas inside millions of tiny sealed cells, so air cannot circulate and moisture cannot wick in. Typical PU insulation has a thermal conductivity (λ) of roughly 0.022–0.026 W/m·K, which is far lower than mineral wool or expanded polystyrene of similar thickness. Exact values depend on the blowing agent and age of the foam, so always request the test report for your project.
The QT-1 is available in three thicknesses: 42 mm, 50 mm and 65 mm. Thicker panels give a longer heat path and more foam, which improves both insulation and stiffness. They are also heavier and need a slightly deeper track and headroom.
Thermal resistance is calculated as R = d / λ (thickness divided by conductivity), and the U-value is U = 1 / R. Using λ = 0.024 W/m·K as an illustrative value for the foam alone:
| Panel thickness | R (m²·K/W) | Ideal panel U (W/m²·K) |
|---|---|---|
| 42 mm | 1.75 | 0.57 |
| 50 mm | 2.08 | 0.48 |
| 65 mm | 2.71 | 0.37 |
These are theoretical panel-only figures. A complete door has higher U-values because joints, hinges, and edges add thermal bridges. For certified whole-door values, look for testing under EN 12428 (thermal transmittance of doors) as part of the EN 13241 product standard.
A perfect panel still loses energy if air leaks around it. Seals decide how much of the panel’s insulation you actually keep.
On the QT-1, sealing rubber is fitted at every panel connection to block the transfer of cold and heat and limit thermal damage at the joint, the weakest point in a sectional door.
The bottom profile carries a threshold EPDM seal, with safety sensors as an option. EPDM stays flexible across a wide temperature range and resists UV and ozone, so it keeps sealing on uneven floors. Perimeter seals close the gap between the panels and the track frame; the 2.0 mm galvanized folded steel track keeps that gap uniform.
Air leakage carries both heat and moisture. Good seals cut drafts, prevent condensation near the floor, and lower the load on HVAC. Air permeability is normally evaluated under EN 12426 and wind resistance under EN 12424 (both linked to EN 13241).
Start with the climate and use: steel for tough industrial traffic, aluminum for corrosive air, 42 mm for moderate climates, 50–65 mm for cold rooms and extreme temperatures. Then check wind class, motor protection, sizes and seal options. Browse our full range of sectional overhead doors, view non-standard doors for special openings, add door accessories, or see logistics equipment for dock solutions. Read how we work, learn about the company in About Us, or explore more industry news.
Cutedoor, based in Zhejiang and active since 1996, designs and produces industrial doors under ISO 9001 and CE certification. Technical sheets are available on the download page.
