In 2025, Egyptian researchers mixed eggshell waste into clay bricks to block the walls from absorbing outside heat and transferring it indoors during hot climates; heat transfer dropped 50%

A pile of discarded eggshells may not seem like something that belongs in a building, but researchers in Egypt have found a way to turn the food waste into part of a potentially useful construction material. In a 2025 study, they mixed powdered eggshell waste into clay and fired the material into bricks designed to slow the movement of heat through walls.

The strongest result came from bricks containing 10% eggshell waste and fired at 1,100°C. Compared with ordinary clay bricks used as the reference material, the modified bricks recorded a 50% reduction in thermal conductivity. The researchers also reported around 30% reductions in thermal diffusivity and thermal effusivity, indicating that the modified material transferred and responded to heat more slowly.

How eggshell waste was turned into bricks

The research team collected eggshells and prepared them before using them as an additive in the clay. The shells were cleaned, dried and ground into a fine powder. The researchers then mixed different amounts of the eggshell powder into clay sourced from Egypt's Kharga Oasis.


The formulations contained varying amounts of eggshell waste, ranging from 1% to 10% by weight. The samples were then fired at high temperatures to produce the modified clay bricks.

The firing process was important because eggshells are largely made of calcium carbonate. When exposed to high temperatures, calcium carbonate decomposes, producing calcium oxide and releasing carbon dioxide.

This process also changes the internal structure of the brick. The eggshell addition contributed to the formation and enlargement of pores within the fired material, giving the bricks a more porous structure.

That matters for heat movement because air trapped within pores conducts heat poorly compared with solid clay. More internal air spaces can therefore make it harder for heat to travel through the brick.

10% eggshell waste produced the biggest thermal change

Among the formulations tested, the brick containing 10% eggshell waste showed the strongest improvement in thermal properties when fired at 1,100°C.

Its thermal conductivity was reduced by 50% compared with the untreated reference clay brick. Thermal conductivity describes how readily heat moves through a material, so a lower value means the material allows less heat to pass through it.

The same formulation also recorded reductions of about 30% in thermal diffusivity and thermal effusivity.

The findings are particularly relevant to buildings exposed to intense heat. In a hot climate, exterior walls can absorb heat from the surrounding environment and transfer some of that heat towards indoor spaces. A material that slows heat movement could help limit this transfer.

However, the study did not establish that buildings using these bricks would consume 50% less electricity for air conditioning or heating. The 50% figure specifically refers to the reduction in thermal conductivity measured for the eggshell-modified brick.

The researchers instead point to the improved thermal properties as having potential to reduce the energy requirements associated with heating and cooling.

Turning food waste into building material

The thermal performance was only part of the attraction. The researchers also highlighted the possibility of using eggshell waste as a resource instead of treating it solely as discarded food waste.

Eggshells are generated in enormous quantities through households and the food industry. Finding uses for this waste in construction could potentially divert some of it from disposal while replacing part of the conventional raw material used in brick production.

In this case, the eggshell powder became part of the brick itself rather than being treated as waste after food preparation.

The approach also changes the internal structure of the brick, meaning the waste material can serve a functional purpose rather than simply acting as a filler.

A promising material, but not yet a finished building solution

The findings do not mean eggshell-based bricks are already ready to replace conventional construction bricks on a large scale.

The study was a laboratory investigation, and the researchers identified the need for further testing of the material's mechanical performance and durability. The modified bricks also showed limitations in compressive strength, meaning more work is needed to determine where and how such materials could safely be used.

That distinction is important because a construction material must do more than insulate against heat. It also needs to withstand loads, weather exposure and long-term use.

Still, the research demonstrates a potentially useful combination: a waste material that changes the physical structure of a common building material while improving its thermal performance.

For hot regions where reducing heat transfer through building walls is important, the findings suggest that discarded eggshells could have a second life inside fired clay bricks.

Rather than simply sending the shells to waste, the researchers have shown how a portion of them could become part of a material designed to slow heat moving through walls.