Thickness is not chosen from a catalogue by room temperature. It follows the temperature difference across the panel — inside air against outside air — and that difference changes with where the room is built.
A −18 °C store in Hanoi and a −18 °C store in Harbin carry the same internal temperature but not the same load. The Harbin room faces −20 °C outside in January; the Hanoi room faces 38 °C. Over a year the two rooms lose heat at different rates, and the panel that is adequate for one is oversized or marginal for the other.
Heat crosses a panel by conduction. The rate depends on three things:
| Factor | What it means in practice |
|---|---|
| Temperature difference | Larger difference, more heat flow, thicker panel |
| Panel core conductivity | PU and PIR differ; density and foam quality matter more than the name |
| Surface area and joints | A room with many panel joints leaks more than the same area with fewer |
The first one is what most specifications are written around. The other two are where cheap panels lose.
A practical starting range, before any calculation:
| Room condition | Difference to outside | Typical thickness |
|---|---|---|
| Chilled, 0 to +5 °C | 30 to 40 °C | 100 mm |
| Frozen, −18 °C | 50 to 60 °C | 150 mm |
| Low temperature, −25 °C and below | 60 °C and above | 200 mm |
| Blast freezer, −35 °C | 70 °C and above | 200 mm, sometimes 220 mm |
Treat these as a starting point, not an answer. Two rooms in the same band can land on different thicknesses once the local summer design temperature and electricity price are in.
Thicker panel costs more once — at purchase. Thinner panel costs more every month — the compressor runs longer to remove the heat that gets through.
The trade-off has a break-even point, and it moves with the price of power:
This is the calculation worth doing, and it needs the local tariff, not a rule of thumb.
When a room will not hold temperature, the panel is not always the cause:
Before adding thickness, check these three. Adding 50 mm to the walls will not fix an unsealed pipe penetration.
To size the panel we need:
With those four, the thickness, the core and the joint detail follow.
No. It follows the difference between inside and outside. A −18 °C room in Hanoi and one in Harbin carry the same internal temperature but not the same load, so the panel that suits one may be oversized or marginal for the other.
Only if every room runs at the same temperature. Most plants hold a chilled room, a frozen store and a blast freezer in one building — three different differences, three different panels.
Not always. It saves running cost, but the saving depends on the local electricity price and the climate. In a mild climate with cheap power the thinner panel can win over ten years; in a hot climate with expensive power the thicker one usually pays back in a few years.
Check the floor insulation, the pipe penetrations and the door traffic before adding thickness. Adding 50 mm to the walls will not fix an unsealed penetration or a door that stands open.
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