Thermal conductivity is one of the most critical material properties in today’s engineering world.

From battery safety and electronics cooling to building insulation and aerospace, knowing how efficiently heat moves through a material determines performance, safety, durability, and cost.

With over 25 years of hands-on experience in thermal analysis and thermal condustivity testing, one thing is clear for our expert Wim Pinnoo:

“No single test method fits all materials”.

Source: Canva

The art of thermal conductivity testing lies in selecting the right method for the right physics.

Where to start?

Two families of thermal conductivity methods

All techniques fall into two main categories:

Steady-state methods - Heat flow is forced through a sample until equilibrium is reached.

Transient methods - Heat is applied briefly and the temperature response is analysed over time.

Each family serves different materials and industries.

Steady-state methods

Heat Flow Meter (HFM)

How it works: A flat sample is clamped between two temperature-controlled plates. Heat flow sensors measure the steady heat passing through.

Where it is used: Foams, mineral wool, insulation boards, construction materials

Pros+

• Easy to apply for low-k materials
• Industrial standard for insulation
• Low operator complexity

Cons-

• Limited flexibility
• Sensitive to contact resistance
• Only standard format flat panels are possible to measure (not suitable for liquids, powders pastes, or thin films; etc.)

Guarded Hot Plate (GHP)

How it works: A precisely heated plate is surrounded by thermal guards to create pure one-dimensional heat flow.

Where it is used: Reference testing of insulation, aerogels, vacuum panels, and building materials

Pros+

• Highest absolute accuracy
• Primary standard for insulation
• Excellent for certification and compliance

Cons-

• Very slow (hours per sample)
• Large and standard format flat solid samples required (not suitable for liquids, powders pastes, or thin films; etc.)
• Not suited for R&D or fast screening

Image GHP - Source NETZSCH

“GHP remains the gold standard for insulation testing.”

Transient methods

Transient Hot Wire (THW)

Othernames for nearly the same method are THB - Thermal Hot Bridge or TLS - Thermal Line Source, all depending the brandname of the instrument manufacturer.

How it works: A thin wire heats and senses the temperature rise inside a fluid or powder.

Where it is used: Liquids, molten polymers, powders, slurries

Pros+

• High accuracy for fluids
• Minimal convection influence for most fluids
• Excellent for high-temperature liquids

Cons-

• Only works for fluid materials within a certain viscosity range (more or less equal to the viscosity of water at 20ᵒC) and some powders & pastes (very dependant their thermal properties)
• Not suitable for solids or composites

Transient Plane Source (TPS)

How it works: A flat sensor acts as both heater and thermometer and is placed between two pieces of material. From the temperature-time curve it simultaneously calculates: thermal conductivity, thermal diffusivity, and volumetric heat capacity.

Image TPS sensor - Source: ThermTest

Where it is used: Solids, foams, powders, polymers, composites, rocks, ceramics, battery materials, TIMs, phase-change materials, etc.

Why TPS stands out:

• Through-plane and in-plane heat flow can be measured
• Thin samples and thick blocks both work
• Very low to very high conductivity range
• Simultaneous Cp measurement improves accuracy
• Minimal sample preparation

Pros+

• Works on almost any solid, paste or powder
• Measures anisotropy (directional heat flow)
• Small samples possible
• Fast and non-destructive

Cons-

• Requires good sensor contact
• Very thin films need special fixtures
• Liquids can be a challenge

“TPS is the widest-applicability thermal conductivity method available today”

Modified Transient Plane Source (MTPS)

How it works: A surface probe applies heat into a single side of the material.

Where it is used: Solids, foams, polymers, quality control or quick test method

Pros+

• Very fast
• Single-sided measurement
• Ideal for production environments

Cons-

• Surface dependent
• Less depth of penetration than TPS

Thermal Interface Material (TIM) method

How it works:

Measures thermal resistance under compression, replicating how thermal pastes, pads, and gap fillers are used in electronics.

Where it is used:

CPU cooling, power electronics, EV batteries

Source: Canva

Pros+

• Best real-world simulation of thermal pastes in electronics
• Includes contact resistance
• Critical for electronics design

Cons-

• Not a true bulk conductivity
• Only for interface materials (and some compressable materials when measuring under pression is required.)

“TIM is the most realistic method for electronics cooling”

Alternative methods

Frequency-Domain (Omega-type) Method

How it works: A modulated heat source creates thermal waves that are analysed in the frequency domain.

Where it is used: Thin films, coatings, layered structures

Pros+

• Excellent for ultra-thin layers
• Good separation of layers

Cons-

• Complex modelling
• Limited bulk material range

DSC - Differential Scanning Calorimetry Method

Some advanced calorimeters use a heat-flow comparison technique to calculate thermal conductivity.

How it works: The DSC method determines thermal conductivity indirectly via heat-flow resistance, allowing measurement of thin polymers, films, and low-conductivity solids using very small sample quantities. Where it is used: Thin films, polymers research materials, where a thermal conductivity instrument isn’t available and a quick indicational value must be determined.

Pros+

• Very small samples
• Simultaneous Cp and phase transitions

Cons-

• Indirect measurement
• Less accurate for absolute conductivity

“According to my knowledge the oldest method to determine thermal conductivity”

Source: Journal of Applied Polymer Science | Wiley Online Library

How to select the right method ?

At EXPERTA | TESTING, we always start from 3 basic questions:

1. What is the material state at the application temperature? → Solid, liquid, powder, paste, foam, composite?
2. How will it be used? → Insulation? Heat spreader/conductor? Interface material?
3. What accuracy is required? → R&D-modelling? product certification? production control?

Best practice selection - Quick Guide

Source: Canva

• Building and insulation → GHP or HFM
• Electronics and thermal pastes → TIM
• Liquids and melts → THW
• R&D across many materials → TPS
• Thin films and coatings → Frequency-domain or DSC-based
• Fast QC → MTPS & TPS

Final thoughts

Why TPS dominates modern materials testing ?

In real-world engineering, materials are anisotropic, layered, porous, and temperature dependent.

And only one technique can measure conductivity, diffusivity, and heat capacity in multiple directions with minimal sample preparation, that’s TPS.

That is why it has become the reference tool for batteries, composites, polymers, phase-change materials, aerogels, and advanced electronics packaging.

What is the best method to measure thermal conductivity ?

“There is no BEST thermal conductivity method, only the best method for your application”

GHP delivers unmatched accuracy for insulation.

TIM provides real-world data for electronics.

TPS offers the widest, most flexible and most informative measurement capability across almost all materials.

Just let us help you with your challenges in Thermal Conductivity testing.

At EXPERTA | TESTING, we combine engineering insight, advanced instrumentation knowledge, and 25+ years of experience to make sure your data truly represents how your material performs in the real world.