Cut your heating bill by 30% just by repainting your walls. Eliminate that cold feeling without major renovation work. Improve your home’s thermal comfort with a simple coat of paint. These are the tempting promises from manufacturers of interior thermal paints.

On paper, it sounds like a dream. They’re selling us a miracle solution that’s quick to apply and without the hassles of traditional insulation. But what’s really going on once you scratch beneath that marketing layer? Between ineffective cheap paints and promising phase-change technologies, it’s time to sort out what actually works from what’s pure sales talk.

Composition and How Microsphere or Aerogel Insulating Paints Work

Basic thermal insulating paints rely on incorporating additives supposedly designed to limit heat transfer through walls. You’ll mainly find two types of materials added to the paint: hollow ceramic microspheres and aerogel particles. Microspheres are tiny air bubbles trapped in a ceramic shell, while aerogel is an ultra-light material made of 99% air in a nanoporous structure.

The theory is simple: Since air is a poor conductor of heat, these additives are supposed to create a thermal barrier. This allows manufacturers to claim that these particles, once integrated into the paint, form an insulating film on the wall. However, the applied thickness remains truly pathetic, generally less than 0.04 inches even after two or three coats by roller or sprayer.

The thermal conductivity announced by manufacturers hovers around 0.030 to 0.050 W/m.K, which seems decent on paper. But here’s where it falls apart: With an application thickness of less than 0.04 inches, the thermal resistance obtained is ridiculously weak. Remember, thermal resistance (R-value) is calculated by dividing thickness by thermal conductivity. So even with the best conductivity in the world, 0.04 inches can’t compete with several inches of insulating material.

Yet these paints are expensive, generally five to ten times more than standard paint. Manufacturers justify this markup with innovative technology and promised energy savings. Unfortunately, independent studies shatter this beautiful marketing construction.

A British study conducted in 2019 according to international standards rigorously tested these paints. And the verdict is damning: The measured thermal performance is no better than simple vinyl wallpaper with its backing. When you factor in all the heat losses in a building, modeling predicts a return on investment of several hundred years. In other words, never.

Research organizations like France’s Centre scientifique et technique du bâtiment haven’t validated manufacturers’ claims for these cheap products. The U.S. Environmental Protection Agency (EPA) explicitly recommends not using these paints as a replacement for conventional insulation due to lack of independent scientific evidence regarding their effectiveness.

Principle and Composition of Phase Change Material (PCM) Paints

Faced with the ineffectiveness of conventional insulating paints, a more sophisticated technology has emerged. These are phase change materials, or PCMs. Unlike microspheres that simply try to slow heat transfer, PCMs exploit a fundamental physical principle to store and release thermal energy.

A phase change material is a substance capable of storing a large amount of energy when it transitions from one state to another, typically from solid to liquid or vice versa. And what makes PCMs interesting is that this transition occurs at a constant or nearly constant temperature. Here’s how it works: When the ambient temperature reaches the material’s melting point, it starts to melt by absorbing heat without its own temperature increasing. Conversely, when the temperature drops, the material solidifies by releasing that heat.

In high-end thermoregulating paints, PCMs are encapsulated in nanometric microcapsules measuring between 10 and 100 nanometers in diameter. These protective polymer capsules isolate the active material from the environment while allowing thermal exchange. There are three main families of PCMs used in buildings: Paraffins (organic compounds from petroleum), salt hydrates (inorganic compounds like sodium sulfate), and fatty acids (organic compounds from plant sources).

The choice of PCM depends mainly on its transition temperature. For residential interior applications, you generally want a phase change temperature between 64 and 77°F, since that’s the typical thermal comfort range. Salt hydrates are particularly appreciated for their low cost and very high volumetric energy storage density, even though they’re harder to encapsulate due to their corrosive and hydrophilic nature.

The energy storage capacity of PCMs is impressive. While it takes only 4.18 joules to raise the temperature of one gram of liquid water by 1.8°F, it takes 340 joules to transform one gram of ice into water at 32°F. PCMs used in thermal paints store about 180 joules per gram during their phase change, more than forty times the sensible heat capacity of water. It’s this energy, called latent heat, that allows the material to effectively regulate temperature.

The operation over a daily thermal cycle is based on a simple principle: During the day, when the indoor temperature rises from sun exposure, heating, or occupant activity, the PCMs gradually melt while absorbing excess heat. This absorption keeps the ambient temperature relatively stable instead of letting heat peaks climb. At night, when the temperature drops, the PCMs solidify by releasing that stored heat, which limits the temperature drop and reduces heating needs.

This technology actually works, unlike microsphere paints. But that doesn’t mean it’s a miracle insulation solution, as we’ll see.

Studies and Numbers on the Real Performance of Phase Change Paints

To objectively evaluate phase change paints, you need to look at studies conducted by independent organizations rather than sales brochures. In France, the CSTB (Centre Scientifique et Technique du Bâtiment) studied the effect of phase change materials integrated into building walls. Their work shows it’s possible to cut temperature peaks in a room by 5 to 9°F thanks to PCMs.

Practically speaking, this means that in an uncooled room where the temperature would normally reach 82°F in summer, using PCMs could maintain the temperature around 73-77°F. That’s significant in terms of thermal comfort, because this difference takes you from an uncomfortable situation to a bearable environment.

Regarding energy savings on air conditioning, university studies report reductions that can reach 30% under optimal conditions. Be careful though with the term “optimal conditions” because these generally involve lightweight construction buildings, with significant temperature variations and intermittent air conditioning use. In a modern well-insulated building with continuous air conditioning, the gains will be much more modest.

Stanford University developed experimental thermoregulating paints combining reflective layers and thermal regulation properties. Their tests under artificial conditions showed reductions in heating needs of 36% and cooling needs of 21%. These impressive numbers need to be qualified because they concern research prototypes under laboratory conditions, not commercial products applied in real-world conditions.

Actually, real-world field feedback is much more nuanced. Sure, PCM paints provide a noticeable improvement in thermal comfort, particularly for eliminating that unpleasant “cold wall” sensation in winter. Sure, humidity regulation is another interesting side benefit. Because by maintaining a more stable surface temperature, PCM paints limit condensation phenomena that can occur on cold walls, thus reducing mold risks and improving indoor air quality.

But let’s also talk frankly about the limitations. Durability is problematic because manufacturers generally recommend renewing the application every 5 to 10 years as effectiveness decreases over time. Microcapsules can rupture, the binder can degrade, and accumulated dirt reduces thermal exchange. This regular maintenance significantly drives up the cost over the building’s lifespan.

The initial price is very high, often ten times more than conventional paint. If you add the costs of regular reapplication and compare them to the energy savings actually observed (generally much lower than the theoretical 30%), the return on investment becomes questionable in most situations.

Effectiveness also depends heavily on climate and building use. PCMs work better in climates with strong day-night temperature swings because this allows the material to complete its charge-discharge cycle. In a very stable climate or with continuously running air conditioning, the benefit decreases significantly.

Our Technical Opinion on Interior Thermoregulating Paints

After analyzing the technology and real performance, it’s time to give a clear technical opinion on the usefulness of interior thermoregulating paints. Let’s start with situations where their use makes no sense.

If your house is already properly insulated with a good thickness of wood fiber, cellulose insulation, or any other high-performance insulation… investing in a thermoregulating paint is a totally unjustified added cost. Structural insulation already does the job effectively and durably. So adding a PCM paint on top will only bring a marginal gain that will never justify its high price or regular maintenance.

And let’s be absolutely clear on one point: A thermoregulating paint, even the best high-end PCM technology, will NEVER replace high-performance structural insulation. The laws of physics are unforgiving. A few fractions of an inch of paint, however sophisticated, can’t compete with 6 to 8 inches of insulation for limiting heat transfer through a wall. Believing otherwise means denying physical reality.

So manufacturers who suggest you can skip traditional insulation thanks to their products are practicing a form of false advertising. Because yes: An insulating paint can improve comfort and modulate temperature variations. But it can’t create a true thermal barrier equivalent to thick insulation.

Now, are there situations where a thermoregulating paint can have real value?

If you’re a renter in a poorly insulated place and you can’t undertake major insulation work, a PCM paint can provide some temporary comfort improvement. It won’t solve the underlying problem (the poor insulation of the dwelling), but it can make your daily life a bit more bearable while waiting for something better. It’s a band-aid, not a solution.

In the case of comfort improvement on a very limited budget, and if you clearly understand you’ll only get a temporary and limited gain, then why not. But you need to go into this with your eyes open, without fooling yourself about miraculous energy savings.

Also be careful not to fall into the “better than nothing” trap. If you have a budget to invest in your home, it’s always better to save a bit longer to do real insulation rather than spend money on a paint that will have to be redone every 5 to 10 years anyway. The cumulative cost of multiple PCM paint applications over 20 years can approach or exceed that of traditional insulation, which will last at least 40 to 50 years.

Cheap microsphere or aerogel paints should be avoided at all costs. No independent study validates their claims. So you’ll literally be throwing your money out the windows (or rather through the poorly insulated walls). Even high-end PCM paints remain a very specific tool for very particular situations and certainly not a universal solution like marketing would have you believe.

Our Conclusion on Interior Thermal Paints

In summary, don’t be seduced by promises of spectacular energy savings with minimal effort. Energy efficiency requires thick solutions, not thin coatings. That’s what the laws of physics say. And to go further, maybe you’ve tested these thermal paints at home? Maybe you have technical questions about their composition or application? Or maybe you have concrete feedback to share with the community? In any case, don’t hesitate to leave a comment below because experience exchanges are often worth more than all the sales brochures in the world.

Technical guides take a long time to create and everyone here is a volunteer. So thanks for taking a few seconds to support the site by buying us a coffee. And thanks also for thinking about sharing this guide around you if it was helpful. We appreciate it 🙂