PIR / PUR rigid foam — properties, λ(T) and computed performance

Service limit ≈140 °C · density 30–50 kg/m³ · EN 14308 · ASTM C591. Supplied as: pre-formed sections, slabs.

Honest assessment

Strengths, limits, verdict

Strengths: best lambda-per-euro in cold service; rigid and light; standard for chilled/cold-water distribution.

Limits: ~140 °C ceiling; combustible (charring); needs vapour barrier detailing at joints in cold service.

Verdict: Cold-side economics winner where fire load is acceptable; cellular glass takes over when water or fire rules tighten.

Thermal conductivity (typical published values)

Mean temperature	λ W/m·K
-30 °C	0.023
0 °C	0.025
20 °C	0.026
50 °C	0.028

λ at mean temperature — rises with T because pore radiation grows with T³.

Computed performance · ASTM C680 simplified

PIR / PUR rigid foam on real pipe sizes

At 100 °C (λ=0.028 at mean)

Pipe	Thickness	Bare W/m	Insulated W/m	Surface	Saving €/m·yr	t CO2/m·yr
DN50	30 mm	152	19	25 °C	€65	0.24
DN50	50 mm	152	14	23 °C	€67	0.25
DN50	100 mm	152	9	21 °C	€69	0.25
DN100	30 mm	287	31	26 °C	€125	0.46
DN100	50 mm	287	21	23 °C	€130	0.47
DN100	100 mm	287	14	21 °C	€133	0.49
DN200	30 mm	551	54	26 °C	€242	0.89
DN200	50 mm	551	36	24 °C	€251	0.92
DN200	100 mm	551	21	22 °C	€258	0.95

Assumptions: 20 °C ambient, still air (h=10 W/m²·K), €0.05/kWh fuel, 8000 h/yr, 82% boiler efficiency, 0.183 kg CO2e/kWh. Your numbers: free calculator.

Against the field

Same duty, all materials — DN100 at 130 °C

Material	λ W/m·K	Loss W/m	Surface	Saving €/m·yr	t CO2/m·yr
Stone wool (mineral wool)	0.043	44	27 °C	€171	0.6
Glass wool	0.040	42	26 °C	€172	0.6
Ceramic fibre (RCF / AES blanket)	0.060	61	29 °C	€163	0.6
Aerogel blanket	0.024	25	24 °C	€180	0.7
Calcium silicate	0.058	59	29 °C	€164	0.6
Expanded perlite	0.062	63	29 °C	€162	0.6
Cellular glass	0.049	50	27 °C	€168	0.6
Microporous (fumed-silica) panels	0.022	23	23 °C	€181	0.7
Elastomeric foam (FEF)	0.040	42	26 °C	€172	0.6
PIR / PUR rigid foam	0.028	30	24 °C	€178	0.7
E-glass needle mat	0.045	46	27 °C	€170	0.6
Silica needle mat / fabric	0.055	56	28 °C	€165	0.6

DN100 pipe at 130 °C, 50 mm insulation, per metre of pipe; bare loss 395 W/m. λ at mean temperature; € and CO2 per metre·year at €0.05/kWh, 8000 h, 82% efficiency. Method: ASTM C680 simplified (h=10).

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FAQ

Questions on this topic

What is the thermal conductivity of pir / pur rigid foam?

Typical published values: 0.023 W/m·K at -30 °C, 0.025 W/m·K at 0 °C, 0.026 W/m·K at 20 °C, 0.028 W/m·K at 50 °C (mean temperature). λ rises with temperature — design with the mean-temperature value, not the ambient one.

What is the maximum temperature for pir / pur rigid foam?

≈140 °C continuous service for typical grades (EN 14308 · ASTM C591). Product-specific limits vary — check the datasheet of the exact grade.

Where is pir / pur rigid foam the right choice?

Cold-side economics winner where fire load is acceptable; cellular glass takes over when water or fire rules tighten.