Thermal Conductivity
Thermal conductivity k measures heat flow through materials. Fourier's Law: q = -k(dT/dx). Silver ~429 W/(m·K), copper ~401, fiberglass ~0.04. R-value = L/k.
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Fourier's Law: q = -k(dT/dx) Q = kA(ΔT)/L for steady state R-value = L/k for insulation Silver and copper best conductors
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Why: Thermal conductivity governs heat loss in buildings, heat sink design, and insulation selection.
How: q = -k(dT/dx). Heat rate Q = kA(ΔT)/L. R-value = L/k. Higher k = better conductor, higher R = better insulator.
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Thermal Conductivity Calculator
Fourier's Law • q = -k(dT/dx) • R-value • Heat Flux
Thermal Conductivity Inputs
Or enter hot and cold temperatures separately below
For educational and informational purposes only. Verify with a qualified professional.
🔬 Physics Facts
Fourier's Law: q = -k(dT/dx)
— Heat Transfer
R-value = L/k; U-value = k/L
— Building Science
Copper 401 W/(m·K), silver 429
— NIST
Fiberglass ~0.04 W/(m·K) insulator
— ASHRAE
📋 Key Takeaways
- • Fourier's Law: q = -k(dT/dx) — heat flux proportional to temperature gradient
- • Silver (429 W/(m·K)) and copper (401) are best conductors; fiberglass (0.04) is a common insulator
- • R-value = L/k (m²·K/W); U-value = k/L (W/(m²·K)) — higher R = better insulation
- • Heat rate Q = kA(ΔT)/L — doubles when area doubles or thickness halves
💡 Did You Know?
📖 How Thermal Conductivity Works
Thermal conductivity (k) measures how well a material conducts heat. Fourier's Law states that heat flux is proportional to the temperature gradient: q = -k(dT/dx). Higher k means heat flows more easily through the material.
Conductors (k > 10)
Metals like copper, aluminum, silver. Heat spreads quickly — ideal for heat sinks, cookware, heat exchangers.
Insulators (k < 0.1)
Fiberglass, foam, aerogel. Heat flows slowly — ideal for building insulation, cold storage, thermal barriers.
🎯 Expert Tips for Thermal Calculations
💡 Use Material Database
Select from the material dropdown to auto-fill k. Values are typical at 20°C — temperature affects conductivity.
💡 Composite Walls
For multiple layers, add thermal resistances: R_total = R₁ + R₂ + ... Then q = ΔT/R_total.
💡 R-value vs U-value
R-value (resistance) — higher is better for insulation. U-value (transmittance) — lower is better. U = 1/R.
💡 Contact Resistance
Real interfaces have contact resistance — use thermal grease or pads to minimize gaps between surfaces.
⚖️ Thermal Conductivity Comparison
| Material | k (W/(m·K)) | Category | Typical Use |
|---|---|---|---|
| Silver | 429 | Metal | Best conductor |
| Copper | 401 | Metal | Heat sinks, wiring |
| Aluminum | 237 | Metal | Heat sinks, cookware |
| Concrete | 1.4 | Building | Walls, foundations |
| Fiberglass | 0.04 | Insulation | Attic, walls |
| Aerogel | 0.015 | Insulation | Spacecraft, extreme |
❓ Frequently Asked Questions
What is thermal conductivity and how is it measured?
Thermal conductivity (k) measures a material's ability to conduct heat, defined by Fourier's Law: q = -k(dT/dx). Units are W/(m·K). High k-values (metals: 50-400 W/(m·K)) conduct heat well; low k-values (insulators: 0.01-0.1 W/(m·K)) resist heat flow. Measured using steady-state or transient methods with controlled temperature gradients.
How does thermal conductivity differ from thermal resistance?
Thermal conductivity (k) is a material property - higher k means better conductor. Thermal resistance (R = L/k) depends on thickness - higher R means better insulator. R-value (m²·K/W) is resistance per unit area. U-value (W/(m²·K)) is thermal transmittance, the inverse of R-value.
Why do metals have high thermal conductivity?
Metals conduct heat via free electrons that move rapidly through the lattice, transferring kinetic energy efficiently. Silver (429 W/(m·K)) and copper (401) have the highest conductivities. Non-metals rely on atomic vibrations (phonons), which are slower, resulting in lower conductivity.
How does temperature affect thermal conductivity?
For metals, conductivity decreases with temperature due to increased electron-phonon scattering. For non-metals, conductivity may increase or decrease depending on material. For accurate calculations, use temperature-dependent k-values from material databases or manufacturer specifications.
What is the difference between R-value and U-value?
R-value (thermal resistance) measures insulation effectiveness - higher is better. Units: m²·K/W or ft²·°F·h/BTU. U-value (thermal transmittance) measures heat transfer rate - lower is better. Units: W/(m²·K) or BTU/(h·ft²·°F). U-value = 1/R-value. Both depend on material thickness and conductivity.
How do I calculate heat transfer through a composite wall?
For multiple layers, add thermal resistances in series: R_total = R₁ + R₂ + R₃ + ... = (L₁/k₁) + (L₂/k₂) + (L₃/k₃) + ... Then heat flux q = ΔT/R_total. Each layer's resistance is calculated separately, then summed. Contact resistance between layers may also need consideration.
What does "HIGH", "MODERATE", and "LOW" mean in the Bloomberg Terminal risk indicator?
The Bloomberg Terminal risk indicator categorizes thermal conductivity levels: "HIGH" (k > 200 W/(m·K)) indicates excellent conductors like metals requiring careful thermal management, typical of heat sinks and thermal interfaces. "MODERATE" (10 < k ≤ 200 W/(m·K)) represents typical building materials and moderate conductors. "LOW" (k ≤ 10 W/(m·K)) indicates insulators suitable for thermal barriers and insulation applications.
How do I choose insulation material for energy efficiency?
Select materials with low thermal conductivity (k < 0.1 W/(m·K)) and high R-value. Common insulators: fiberglass (0.04), mineral wool (0.04), polyurethane foam (0.02), aerogel (0.01). Consider thickness, cost, moisture resistance, and fire safety. Higher R-value means better insulation performance.
📊 Thermal Conductivity by the Numbers
📚 Official Data Sources
⚠️ Disclaimer
This calculator is for educational and engineering design purposes. Thermal conductivity values vary significantly with temperature, pressure, moisture content, and material composition. Material k-values provided are typical ranges and may differ from actual values. For critical applications (building insulation, heat exchangers, thermal management), consult manufacturer specifications and use validated material databases (NIST, ASHRAE). Always account for temperature-dependent properties, contact resistance, and real-world conditions. For building energy analysis, use certified software and comply with local building codes.
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