Table of Contents
Basics of thermal insulation
Thermal insulation means the targeted reduction of heat transfer between areas of different temperatures. Inside buildings, it protects against heat in summer and cold in winter. The largest investments are made in the building, packaging and industrial sectors, but clothing and animal fur also work according to the same principle. The aim is always to reduce heat conduction in particular, but also convection and radiation as much as possible.
The most important parameter is the thermal conductivity (λ, lambda) of a material. It indicates how easily heat is transported through a material. The lower the thermal conductivity λ, the more effective the material is as an insulating material.
Thermal conductivity & insulation materials in comparison
The thermal conductivity describes how much heat flows through a material. Very low values (between 0.013 and 0.040 W/m-K) are found in foams, mineral wool and aerogels. Stone, concrete or metal, on the other hand, insulate very poorly. The majority of common insulating materials (PUR, EPS, rock wool, glass wool) use air pockets (pores) to reduce the heat flow. Materials made from renewable raw materials such as wood fiber, hemp or cellulose are becoming increasingly popular as they offer additional ecological benefits (Verbraucherzentrale 2025)
Examples of thermal conductivities and typical applications:
| insulation material | Type | λ value [W/m·K] | Typical application |
|---|---|---|---|
| air | gas | 0,026 | window |
| Polyurethane (PUR) | rigid foam | 0,025–0,030 | Plates, pipes, tanks |
| EPS (styrofoam) | polystyrene | 0,030–0,040 | Facades, packaging |
| rock wool | mineral fiber | 0,035–0,045 | Roofs, walls, facades |
| glass wool | mineral fiber | 0,032–0,040 | Roofs, walls, facades |
| aerogel | high tech | 0,013–0,020 | Windows, special applications |
| Wood fiber, hemp | natural fiber | 0,040–0,050 | eco-construction |
U-value and R-value
The U-value (heat transfer coefficient) is given in W/m²-K. It describes how much heat energy is lost per second through one square meter of a building component when the temperature difference is 1 degree. A low U-value means good insulation.
The thermal resistance or R-value (K-m²/W) is the reciprocal of the heat transfer coefficient (U-value). It is calculated by dividing the thickness of a component in meters by its thermal conductivity.
Practical recommendation 2025:
- New exterior walls ≤ 0.24 W/m²-K
- Refurbishments often ≤ 0.20 W/m²-K (Energy Experts 2025)
Example calculation:
For a wall with 20 cm EPS insulation, λ = 0.035 W/m-K:
R = 0.20 m / 0.035 W/mK = 5.71 K⋅m2/W
U = R-1 =0.18 W/m2K
Both current requirements are therefore fulfilled.
However, insulation with a glass wool thickness of 20 cm at λ = 0.045 W/m-K only meets the requirements for new external walls:
R = 0.20 m / 0.045 W/mK = 4.44 K⋅m2/W
U = R-1 =0.23 W/m2K
Areas of use and practical applications
Construction & renovation: Depending on requirements, EPS (polystyrene), PUR rigid foam and mineral wool are used in the construction industry. Modern renovations and new buildings are increasingly relying on ecological materials such as wood fiber or cellulose. Polyurethane foam dominates in the insulation of hot water pipes and tanks.
Packaging: For cold chains (food, vaccines, etc.), multi-layer insulation materials, thermofoils and vacuum technology are used.
Clothing & everyday life: High-quality winter clothing uses the insulating effect of the trapped air in fiber or down fillings. Animal fur, feathers and sandwich materials for sleeping mats also work on the same principle.
Modern measuring methods
Heat Flow Meter (HFM): Measurement of the amount of heat flowing through a material sample at a defined temperature difference. Ideal for insulating panels and building materials – delivers reliable results relatively quickly for practical use and production.
Guarded Hot Plate (GHP): Reference method for maximum measurement accuracy. Particularly useful for exact comparative measurements or in research. This method is used in particular for high measuring temperatures.
Transient Hot Bridge (THB): This is by far the fastest measuring method and enables efficient testing of even small materials. Particularly useful for development and quality assurance.
Sustainable insulation materials & eco trends
Sustainability is also a key trend in insulation materials. In addition to wood fibers, hemp, cellulose, cork and sheep’s wool, recyclable rigid foams are also being used. In addition to their insulating properties, characteristics such as carbon footprint, resource conservation and recyclability are playing an increasingly important role. The use of many ecological materials is subsidized by the state (Energy Experts 2025).
Conclusion
Successful thermal insulation requires in-depth knowledge of materials, up-to-date knowledge of standards and the use of modern measurement methods. With ecological solutions, practical tables, scientific methodology and consideration of all legal framework conditions, high energy efficiency and sustainable building value can be ensured.
List of sources
- 42Watt (2024): EU refurbishment obligation
- Consumer advice center (2025): Ecological thermal insulation with alternative insulation materials | Verbraucherzentrale.de
- Energy experts (2025): Thermal insulation – funding & materials
- BAFA (2025): Eligible costs – BEG
