For PU sandwich panels, the common thickness rule is 75 mm for chillers at 0 to +10 °C, 100 mm for rooms from about −5 to −18 °C, 120 mm for frozen storage at −18 to −25 °C, 150 mm for blast freezers at −30 to −40 °C, and 200 mm for ultra-low temperatures down to −60 °C. Move one step thicker when the design ambient is above about 40 °C or the room stands in direct sun.
The sections below explain how thickness affects heat gain, energy cost and surface condensation, and which other panel specifications matter as much as thickness.
Which panel thickness should you use for each room temperature?
| Room temperature | Typical application | PU thickness | U-value at λ 0.022 W/m·K |
|---|---|---|---|
| +5 to +15 °C | Flower rooms, wine, process and packing rooms | 50–75 mm | 0.44–0.29 W/m²·K |
| −5 to +5 °C | Fruit, vegetables, dairy, fresh meat chill | 75–100 mm | 0.29–0.22 W/m²·K |
| −18 to −20 °C | Frozen food storage | 100–120 mm | 0.22–0.18 W/m²·K |
| −20 to −25 °C | Ice cream, long-term frozen fish and meat | 120–150 mm | 0.18–0.15 W/m²·K |
| −30 to −40 °C | Blast freezers, quick-freeze tunnels | 150 mm | 0.15 W/m²·K |
| −40 to −60 °C | Tuna and sashimi-grade storage, laboratory freezers | 200 mm | 0.11 W/m²·K |
The U-value column assumes a declared PU core conductivity of 0.022 W/m·K. Aged foam, lower density or poor joints raise the effective value, so allow some margin in load calculations.
How does panel thickness affect heat gain?
Heat flow through a panel is Q = U × A × ΔT, and U = λ ÷ thickness. Doubling the thickness halves the transmission heat. At a typical freezer temperature difference of 53 K (35 °C outside, −18 °C inside), heat gain per square meter is:
- 100 mm: 0.22 × 53 ≈ 11.7 W/m²
- 120 mm: 0.183 × 53 ≈ 9.7 W/m²
- 150 mm: 0.147 × 53 ≈ 7.8 W/m²
The benefit of each extra 20–30 mm shrinks as panels get thicker. That is why 200 mm is reserved for very low temperatures where ΔT is large enough to justify it.
Is a thicker panel worth the extra cost?
Consider a 6 × 5 × 3 m freezer with 126 m² of panel surface at −18 °C and 35 °C ambient. Moving from 100 mm to 120 mm reduces transmission by about (0.220 − 0.183) × 126 × 53 ≈ 0.25 kW. Running all year with a system coefficient of performance (COP) of about 1.8 at freezer conditions, that saves roughly 0.25 × 8,760 ÷ 1.8 ≈ 1,200 kWh per year. At an electricity price of USD 0.12/kWh, the saving is about USD 145 per year, plus a slightly smaller condensing unit.
Use your own tariff and ambient to repeat this quickly. In hot climates with high tariffs, the thicker option often pays back within a few years. In mild climates with cheap power, the standard thickness is usually adequate.
Can a cold room panel be too thin even if the load calculation works?
Yes. The second check is surface condensation on the warm side. If the outer skin falls below the dew point of the surrounding air, it will sweat, causing corrosion, mold and dripping. The outer skin temperature drop is approximately U × ΔT divided by the outside surface coefficient (about 8 W/m²·K for still indoor air).
- 100 mm freezer panel: 0.22 × 53 ÷ 8 ≈ 1.5 K below ambient.
- At 35 °C and 80% RH the dew point is about 31 °C, so a skin at about 33.5 °C stays dry.
Well-made flat panels rarely sweat. Condensation problems almost always appear at thermal bridges: badly sealed joints, metal fixings that cross the insulation, door frames without heater wire, and the floor-to-wall junction. Thickness cannot fix poor detailing.
What else matters besides thickness?
Core material and density
| Core | Typical λ (W/m·K) | Notes |
|---|---|---|
| PU (polyurethane) | 0.022–0.024 | Standard for cold rooms; density around 38–42 kg/m³ |
| PIR (polyisocyanurate) | 0.022–0.023 | Better fire performance than standard PU; often specified where codes require it |
| EPS (expanded polystyrene) | 0.035–0.040 | Lower cost; needs much greater thickness for the same U-value |
Ask for the foaming method (high-pressure injection gives a more uniform core), core density and declared conductivity. A cheaper panel with lower density can look identical on a quotation but perform worse.
Skin material
- Pre-painted galvanized steel (PPGI), typically 0.4–0.6 mm, for most food storage.
- Stainless steel (SS304) for wet areas, meat and seafood processing, and frequent washdown.
- Embossed aluminum where light weight and corrosion resistance are priorities.
Joint type
Camlock panels use eccentric hooks foamed into the panel edges, pulled tight with a hex key. They give fast, repeatable assembly and can be dismantled and relocated. Tongue-and-groove panels are common for larger warehouse buildings where panels are fixed to a steel structure. Either way, joints need sealant on the warm side to act as a vapor barrier.
Floor construction
Small chillers can use insulated floor panels with a reinforced top layer. Freezers at −5 °C and below built directly on ground need floor insulation plus frost-heave protection—heating cables or ventilation pipes under the insulation—because the soil beneath can freeze and lift the slab over time. For forklift traffic, use a structural concrete floor over insulation rather than floor panels.
Should the door match the panel thickness?
Yes. Hinged and sliding cold room doors should use the same insulation thickness as the walls, with a heated frame on freezer doors to stop the gasket freezing. Freezers also need a pressure relief valve: when warm air enters and cools, the internal pressure falls and can make the door hard to open or stress the panels.
How does climate change the right thickness?
The thickness table assumes a design ambient of about 30–35 °C with the room indoors. Hotter sites and outdoor rooms see a larger temperature difference across the panel and, on sunny walls and roofs, surface temperatures well above air temperature. A practical adjustment is:
| Site condition | Suggested adjustment |
|---|---|
| Indoor, air-conditioned building | Standard thickness; lower end of the range is often acceptable |
| Indoor, unconditioned warehouse at 30–35 °C | Standard thickness |
| Ambient regularly 40–46 °C | One step thicker, for example 120 mm instead of 100 mm for −18 °C |
| Outdoor room in direct sun | One step thicker plus a ventilated roof or sunshade over the ceiling panels |
| High humidity coastal or tropical site | Standard or one step thicker, with careful sealing of joints to prevent condensation |
How does panel thickness affect the refrigeration equipment?
Thicker panels reduce transmission load, which can allow a smaller condensing unit and evaporator. For small rooms, the saving is often less than one equipment size step, because product and infiltration loads remain unchanged. For large frozen stores, where transmission can be 30–50% of the total load, a thicker panel can reduce compressor capacity noticeably and lower daily running hours.
The reverse is also true: if a buyer chooses thinner panels to reduce upfront cost, the refrigeration system must be sized for the higher heat gain. Make sure the panel thickness used in the load calculation is the same thickness that appears on the purchase order.
How do you specify panels on a request for quotation?
- Room internal dimensions and the temperature of each chamber.
- Panel thickness for walls, ceiling and floor (or say "no floor" if building on an insulated slab).
- Skin material and thickness for inner and outer faces, plus color.
- Core type (PU or PIR) and any fire-rating requirement from local codes.
- Door type, clear opening size, and accessories such as strip curtains, viewing windows and ramps.
- Site ambient temperature and whether the room is indoors or outdoors.
Our cold room panels are supplied in the thicknesses above with camlock joints, matched doors and accessories. To check whether your chosen thickness suits the room and climate, see our guide to the full refrigeration load and then send us your layout for a quotation with matched condensing units.
Frequently asked questions
What thickness is a standard freezer room panel?
For frozen storage at −18 to −20 °C, 100–120 mm PU panels are standard, and 120 mm is the safer choice in hot climates. Rooms at −25 °C usually use 120–150 mm.
Is 100 mm panel enough for a −18 °C cold room?
It can be in mild climates and indoor locations. Where ambient regularly exceeds about 40 °C or the room is outdoors in sun, 120 mm reduces energy use and condensation risk enough to justify the cost.
What is the U-value of a 150 mm PU panel?
With a core conductivity of 0.022 W/m·K, a 150 mm panel has a U-value of about 0.15 W/m²·K. Real installed values are slightly higher because of joints and fixings.
Do chiller rooms need floor insulation?
Rooms at 0 to +5 °C on an indoor slab often use insulated floor panels or a thin insulated screed. Freezers on ground always need floor insulation and protection against frost heave.
