Conventional thermal insulation works against two transport mechanisms: it slows down heat conduction through the building component and prevents convection within the construction. Hence the simple rule: insulation performance needs thickness — the lower the thermal conductivity and the thicker the layer, the better the U-value.
For some years now a different approach has been under discussion: ultra-thin coatings that target the third transport mechanism — thermal radiation. Instead of slowing the heat flow, they are meant to reflect infrared radiation before the energy leaves the component. A fundamentally different operating principle from an external thermal insulation composite system (German: WDVS, internationally known as ETICS).
How it is supposed to work
Suppliers such as IsoFireTec offer such coating systems for external facades, interiors and — as a transparent variant — for listed, heritage-protected surfaces. According to the manufacturer's specifications, the coating reflects 88 to 95 per cent of thermal radiation (infrared range) and is thus meant to block rather than delay energy loss; the layer thickness is measured in millimetres instead of centimetres.
According to the manufacturer, the coating is also eligible for subsidies. Whether a specific funding route holds up in an individual case should, however, be clarified with an energy consultant and the funding body before commissioning — the individual measures under the German federal funding scheme for efficient buildings (BEG) require recognised performance values and minimum U-values (see below).
Important for context: these are the manufacturer's own figures. Independent, standards-grade confirmation is still outstanding.
What the experts say
Within the German trade bodies the principle is currently the subject of critical debate:
- The Research Institute for Thermal Insulation (FIW München) expresses fundamental doubts that the advertised performance values and savings would withstand scientific scrutiny.
- Studies, including by the Institute of Building Physics at Leibniz University Hannover, have so far concluded that "energy-saving paints" are "energetically ineffective"; consumer advice centres also warn against exaggerated advertising claims.
- Decisive in practice: for such coatings there is no recognised design value of thermal conductivity. They therefore cannot be used in compliance calculations under the German Buildings Energy Act (GEG) or in the energy performance certificate — anyone who needs to fulfil a refurbishment obligation or apply for subsidies currently has no way around conventional insulation.
The field test is under way
Precisely because laboratory values and manufacturer claims diverge, the housing industry is currently running field trials under real-world conditions. A typical test set-up: three comparable building volumes are operated in parallel — one receives only a conventional paint coat, one a classic ETICS, one the new nano coating. Before the measure, heat meters are installed so that a genuine before-and-after comparison of heating energy consumption is possible — over several heating seasons, with weather adjustment.
That is the right way to do it: not data sheet against data sheet, but measured heat quantities on the real building. Until these results are available, the technology must be classified as experimental.
Why the approach is interesting nonetheless
Should a relevant effect be reliably confirmed, the principle would have tangible advantages over a classic ETICS:
- Fire protection: a millimetre-thin, mineral-based coating sidesteps the fire-safety issues of thick polystyrene systems (fire barriers, requirements for building classes and special-purpose buildings).
- Facade build-up and detailing: no build-up of 12–20 cm of insulation thickness — window reveals and wells keep their depth and daylight, junctions to roof, plinth and parapet remain simple, setback distances and roof overhangs do not become a problem.
- Existing buildings and heritage: application without a major scaffolding operation, preservation of facade articulation and appearance.
- Weight and logistics: no additional load package on the facade, fast application.
Our assessment
For owners and asset holders, as things stand today: the IR-reflective coating is no substitute for an ETICS — neither in GEG compliance calculations nor in the subsidy landscape. Anyone wanting to trial the approach should do it the way the current field trials demonstrate: define a pilot area, install heat meters beforehand, measure over several heating seasons. Without a measurement concept, any statement about the effect remains speculation.
The debate about new insulation technologies does, however, direct attention to a more fundamental question: is wrapping the building actually always the best way? In our view: not necessarily. A refurbishment decision should look at the building holistically — envelope and building services together — and soberly weigh costs and benefits for each measure. In many existing buildings, the combination of window replacement (the windows are at the end of their service life anyway) and insulating the basement ceiling and the top-floor ceiling — both comparatively simple and inexpensive to implement — delivers more effect per euro invested than an elaborate ETICS. Well-preserved, architecturally appealing rendered facades can then remain what they are. What matters is the interaction with heating efficiency: the envelope must be upgraded to the point where the building services operate economically — and no further.
And one factor is underestimated in almost every refurbishment concept: the occupant. A building can be insulated ever so well and fitted with the most modern heating system — if a window is permanently tilted open in winter, the heat is lost unused and the calculated efficiency never shows up in actual consumption. The occupant is therefore always a co-deciding factor in the success of a refurbishment concept; serious planning thus includes realistic assumptions about user behaviour — and, after the refurbishment, a short briefing on how the building is meant to work (purge ventilation instead of tilted windows, how to handle the controls).
A critical word on the subsidy landscape belongs in this assessment: the current funding regime in Germany puts a one-sided focus on the heat pump when it comes to heating replacement. In our view, this means genuine technology and price competition in the market does not currently exist — experience shows that high subsidy rates for one technology prop up suppliers' prices and narrow the solution space instead of opening it. All the more important is a subsidy-independent cost-benefit calculation per building: only when a measure is technically and economically sound even without a grant is the subsidy what it should be — an accelerator, not a sales argument.
Here, too, the basic principle of every serious refurbishment decision shows itself: a condition survey and thorough groundwork are essential in order to assess costs, risks — and in this case: actual effects — sensibly.
Planning a facade refurbishment and want to know which insulation strategy suits your building? We assess the existing fabric with an open mind on technology — based on measured values instead of advertising claims.
Related articles:
- GEG 2024/2026: Refurbishment Obligations and Exceptions for Existing-Building Owners
- Building Thermography: When It Is Worth It, What It Shows – and Where Its Limits Lie
- iSFP 2026: Refurbishment Roadmap, BAFA Subsidy and the 5% Bonus Explained
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Would you like this topic assessed for your property in concrete terms? I offer a free initial consultation — fee ranges, scope and available subsidies discussed openly.