A new analysis has found that phase change materials can significantly reduce building energy use when placed precisely within walls, ceilings, and floors.
That finding recasts ordinary building surfaces as active thermal regulators that can stabilize indoor temperatures before heating and cooling systems engage.
Why placement matters
Across more than 3,300 records on walls, roofs, ceilings, and floors, the same pattern kept surfacing in how these materials performed.
Analyzing that body of evidence, Prof. Frédéric Kuznik at INSA Lyon demonstrated that placement and material choice directly determine whether stored heat alters indoor conditions.
Performance rose or collapsed depending on whether the material reached its melting point at the right moment within a building’s daily temperature cycle.
This constraint shows that storage capacity alone cannot guarantee impact, setting up the need to understand how these materials manage heat in practice.
PCMs in building walls
Engineers call them phase change materials (PCMs), heat-storing compounds that melt and harden near a target temperature.
During melting, latent heat, energy absorbed without raising temperature, lets a wall soak up warmth instead of passing it indoors.
Organic blends often behave predictably, while salt hydrates, salts that store water within crystals, can move heat faster.
The tradeoffs explain why no single recipe fits every building, climate, budget, or safety target.
What buildings gain from PCMs
Heating and cooling still dominate building energy demand, so even small delays in heat flow can pay off quickly.
In field and lab tests, PCM mixed into fiber insulation cut heat flow by about 30%.
Another year-long comparison found a 54% improvement in thermal comfort between similar buildings, one with PCM and one without.
Comfort gains matter most where occupants feel sharp afternoon spikes or cold-night drops, because comfort improves before bills fully respond.
Matching local weather
Climate decides whether PCM ever cycles properly, because a material that never fully melts or freezes cannot store much.
Work in Kazakhstan found that a melting point near 79 degrees Fahrenheit delivered 39.1% summer efficiency in a modeled building.
Across six Kazakh cities, optimized selection pushed thermal energy efficiency about 37% higher, showing how strongly local weather matters.
Designers therefore need climate data as much as material data, especially in places with large day-night temperature swings.
Putting PCM inside ceilings
Once the chemistry looks right, the harder problem is getting PCM into plaster, concrete, or panels without leaks.
Direct mixing is simple, but liquid seepage and chemical reactions can weaken bonds in highly alkaline building materials.
Encapsulation, sealing PCM inside a shell, helps because heat moves while the liquid stays put.
Price and performance both follow encapsulation choice, since smaller capsules spread heat better but usually cost more.
Best spots indoors
Gypsum boards are popular because they already sit in partitions and ceilings where indoor swings first show up.
Tests summarized in the review found rooms stayed above 82 degrees Fahrenheit for only five hours, compared with 50 hours in standard rooms.
On roofs, pairing PCM with a reflective surface reduced heat flux by 66.8% and lowered surface temperature by about 4 degrees Fahrenheit.
Performance differences like that explain why location matters so much: different building layers see very different heat patterns.
Moving heat faster
PCM works only as fast as heat can reach it, and that remains one of the field’s biggest limits.
Some researchers boosted thermal conductivity, the ease of moving heat, by adding graphite, metal oxides, or carbon nanotubes.
Recent studies summarized in the review reported thermal-conductivity gains of 40% to 150%, speeding charging and discharging inside building materials.
Faster heat flow can make smaller PCM layers useful, but extra additives may raise cost or complicate manufacturing.
Durability and risk
Real buildings punish materials for years, so fire risk, leakage, and repeated cycling decide whether promising lab results survive.
Organic PCM can burn more easily, while some salt hydrates suffer supercooling, delayed freezing that slows heat release when rooms cool.
Repeated expansion can also crack nearby material or separate mixed ingredients, which steadily reduces storage after many cycles.
Fire risk, leakage, and cycling damage help explain why standardized fire tests and long-term trials still lag behind laboratory progress.
Next steps for PCMs in buildings
Cost still blocks large projects, especially when designers load walls beyond about 10% to 20% PCM by weight.
Bio-based blends and cheaper mineral carriers look promising because they can lower material cost and reduce fire concerns.
One recent composite stayed stable after 2,000 cycles, pointing toward more practical products for real buildings.
Even so, builders need codes, supply chains, and side-by-side field data before hidden thermal storage becomes routine.
The evidence shows that PCM succeeds when chemistry, climate, and placement line up with the daily rhythm of heat.
Used well, PCM can turn ordinary walls and roofs into built-in thermal storage, but poor matching still wastes money and space.
The study is published in Thermal Science and Engineering Progress.
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