Instead of the vague assumption that thicker is better, understanding thermal conductivity (λ) and thermal resistance (R) lets you get more insulation performance from the same budget. This guide compares the numbers directly across the materials most used on industrial sites.
The key metrics — λ and R
| Thermal conductivity λ (W/mK) | Lower is better. It describes the material's own ability to transfer heat — an intrinsic property independent of thickness or area. |
| Thermal resistance R (m²K/W) | Higher is better. R = thickness (m) ÷ λ. For the same material, R rises with thickness. |
| Thermal transmittance U (W/m²K) | Lower is better. U = 1 ÷ R. The unit most often used in building energy standards. |
Thermal conductivity compared
The figures below are representative values at ambient temperature (25°C). λ rises with temperature — performance falls — so for hot service you must always check the λ value at the actual operating temperature.
| Aerogel felt | λ ≈ 0.015 W/mK ★ the lowest available |
| PIR urethane pipe insulation | λ ≈ 0.022 W/mK |
| PUR urethane foam | λ ≈ 0.025–0.030 W/mK |
| Rubber foam (NBR) | λ ≈ 0.033–0.038 W/mK |
| Mineral wool 80K | λ ≈ 0.030–0.036 W/mK |
| Glasswool 32K | λ ≈ 0.033–0.040 W/mK |
| Glasswool 64K | λ ≈ 0.030–0.035 W/mK |
| Cerakwool 128K (at 300°C) | λ ≈ 0.060 W/mK (hot condition) |
| EPS (expanded polystyrene) | λ ≈ 0.031–0.040 W/mK |
| Cellular glass (Foamglas) | λ ≈ 0.040–0.055 W/mK |
R value at 50 mm
Calculating R at a common thickness of 50 mm makes the real performance difference tangible. R = 0.05 m ÷ λ
| Aerogel 50 mm | R ≈ 3.33 m²K/W — the highest |
| PIR urethane 50 mm | R ≈ 2.27 m²K/W |
| PUR urethane 50 mm | R ≈ 1.85 m²K/W |
| Mineral wool 80K 50 mm | R ≈ 1.47 m²K/W |
| Glasswool 32K 50 mm | R ≈ 1.35 m²K/W |
| Rubber foam 50 mm | R ≈ 1.39 m²K/W |
Thickness required for the same R value
To reach a target R value of 2.0 m²K/W, each material needs the following thickness.
| Aerogel | About 30 mm ✅ |
| PIR urethane | About 44 mm |
| PUR urethane | About 55 mm |
| Glasswool 32K | About 74 mm |
| Mineral wool 80K | About 66 mm |
| Rubber foam | About 70 mm |
Aerogel achieves the same insulation performance as glasswool at less than half the thickness. That is precisely why it is specified where pipe spacing is tight or thickness is constrained.
How λ changes with temperature — take care in hot service
The λ value of insulation rises as temperature rises. Applying a catalogue figure quoted at ambient temperature to hot plant can leave you with far less performance than expected.
| Glasswool 32K at 25°C | λ ≈ 0.036 W/mK |
| Glasswool 32K at 200°C | λ ≈ 0.075 W/mK (more than double) |
| Mineral wool 80K at 25°C | λ ≈ 0.033 W/mK |
| Mineral wool 80K at 400°C | λ ≈ 0.110 W/mK |
| Cerakwool 128K at 25°C | λ ≈ 0.042 W/mK |
| Cerakwool 128K at 800°C | λ ≈ 0.230 W/mK |
| Aerogel at 25°C | λ ≈ 0.015 W/mK |
| Aerogel at 300°C | λ ≈ 0.030–0.040 W/mK (still lower than the alternatives) |
Selecting on performance
- No thickness constraint, minimise cost → glasswool or mineral wool (λ 0.030–0.040)
- Reduce thickness, mid-range budget → PIR urethane pipe insulation (λ 0.022)
- Thickness must be minimised, high performance needed → aerogel (λ 0.015)
- Cryogenic lines (from −196°C) → PIR urethane or aerogel
- Above 300°C → mineral wool (always check the λ value at temperature)
- Above 800°C → Cerakwool (design the thickness on the hot-condition λ value)
✅Tell us your service temperature, pipe size and the insulation thickness you can accommodate, and we will produce a comparison table and calculate the appropriate thickness. Technical advice: +82 10-4266-9745
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