Insulation slows heat; it does not create cooling. PUR foam limits conduction, closed cells limit gas movement and sealed joints limit air leakage.
In short: core thickness matters, but doors, joints and penetrations often become the weak points.
Typical PUR conductivity is about 0.022–0.024 W/(m·K); use the current panel declaration for design.
The three mechanisms of heat transfer
Heat moves from hot to cold by three distinct mechanisms. An effective panel addresses all three at once, and each maps to a specific feature of the panel construction.
| Mechanism | What it is | How the panel defeats it |
|---|---|---|
| Conduction | Heat carried through a solid by molecular vibration. Rate set by thermal conductivity λ (W/m·K) — lower is better. | A low-λ foam core and a single continuous foam path with no metal spanning skin-to-skin. |
| Convection | Heat carried by moving air — warm air rises, cold sinks, and the circulation transports energy. | The closed-cell foam structure traps gas so it cannot circulate; gaskets stop air moving across joints. |
| Radiation | Heat emitted as electromagnetic waves by every surface above absolute zero. | The continuous, opaque steel skins block direct radiant exchange with the surroundings; once the room is enclosed, radiation is a minor heat path compared with conduction and air leakage. |
Conduction and the λ-value
Conductivity is the property that ranks an insulator. The lower the λ-value, the slower heat passes through a given thickness.
| Material | λ (W/m·K) | Verdict |
|---|---|---|
| Steel | ~50 | Excellent conductor (a thermal-bridge risk) |
| Concrete | ~1.7 | Poor insulator |
| Glass | ~1.0 | Poor insulator |
| Wood | ~0.12 | Moderate |
| Expanded polystyrene (EPS) | ~0.038 | Good |
| Still air | ~0.025 | Excellent (if it cannot move) |
| Polyurethane (PUR), ~40 kg/m³ | ~0.022–0.024 | Excellent |
Rigid PUR foam reaches near-still-air conductivity by locking gas inside millions of sealed closed cells. Because the gas cannot convect, only slow conduction through the thin cell walls and trapped gas remains — which is why a few centimetres of foam outperform a thick masonry wall.
Algor core note: Frostbox panels (MTH "Algor" line) use a polyurethane (PUR) core, not PIR. Treat λ ≈ 0.022–0.024 W/m·K as a typical-PUR engineering figure for calculation, not a quoted manufacturer guarantee — request the MTH datasheet for project-critical values.
Good insulation is a chain
The weakest link sets the result:
- Pick the right λ and thickness for your target temperature — that fixes the panel U-value and the unavoidable transmission load.
- Defeat all three mechanisms — closed-cell foam (conduction + convection), continuous opaque steel skins (radiation), compressed gaskets (joint convection).
- Detail the bridges — joints, doors, penetrations, and floor junctions decide whether the theoretical U-value survives contact with a real site.
A tighter envelope lets you specify a smaller, cheaper refrigeration unit that cycles less and lasts longer. To turn panel performance into the numbers that size a system, read R-value and U-value explained; for where rooms actually leak, see Thermal bridges in cold rooms.
Related articles
- R-value and U-value explained
- Thermal bridges in cold rooms
- Heat load calculation
- Panel specifications
- Choosing the right cold room
λ figures above are typical PUR engineering values for design and comparison; project-critical specifications for the MTH Algor panel system are available on request — contact [email protected].
