MATERIALS
Thermal Conductivity (k-value)
Heat conducted through a unit thickness of material per unit area per °C temperature difference, in W/m·K
Also calledthermal conductivityk valuek-valuelambdalambda value
Related on InfraLens
Definition
Thermal conductivity (symbol k or λ) measures how fast heat flows through a material. Units: W/m·K. Low k = good insulator (rockwool 0.038), high k = good conductor (aluminium 211, steel 50). The fundamental input to U-value and R-value calculations. Determined per IS 3346:1980 (guarded hot-plate method).
Typical values
PUR foam0.022-0.028 W/m·K
EPS / XPS0.030-0.040 W/m·K
Rockwool0.035-0.045 W/m·K
AAC block0.16-0.22 W/m·K
Brick masonry0.81 W/m·K
Concrete (dense)1.74 W/m·K
Steel50 W/m·K
Aluminium211 W/m·K
Where used
- U-value and R-value computation
- Insulation thickness sizing
- HVAC load calculation
- ECBC envelope compliance
Acceptance / threshold
Per IS 3346: k determined by guarded hot-plate apparatus on representative samples; manufacturer test report or third-party lab cert accepted.
Site example
For 100 mm rockwool (k = 0.038), thermal resistance R = thickness / k = 0.1 / 0.038 = 2.63 m²K/W. To hit ECBC roof U-value 0.4 W/m²K (R = 2.5), 100 mm rockwool is sufficient.
Frequently asked
What is thermal conductivity (k-value)?
Thermal conductivity k measures how easily heat flows through a material per unit thickness per °C, in W/m·K. Low k = good insulator. Determined per IS 3346 by guarded hot-plate method.
What is a good k-value for insulation?
Below 0.05 W/m·K is considered insulation-grade. Rockwool 0.038, EPS 0.035, XPS 0.032, PUR foam 0.025 — all well below the threshold. Compare to brick (0.81) — over 20× worse.
Related materials terms
Ordinary Portland Cement (OPC)
33/43/53 grade Portland cement. 53 most common for structural use.
Portland Pozzolana Cement (PPC)
Cement blended with fly ash. More durable than OPC.
Portland Slag Cement (PSC)
Cement blended with blast furnace slag
Aggregates (Fine & Coarse)
Coarse (10-40mm) and fine (sand) aggregates per IS 383
Sand (River / M-Sand)
Fine aggregate. River sand or manufactured sand.
Brick / Block Masonry
Bricks per IS 1077, blocks per IS 2185
Tile (Floor / Wall / Roof)
Floor/wall/roof tiles per various IS codes
Paint & Coatings
Wall paint, primer, putty, coatings