Superhydrophobic materials—often called “never-wet” surfaces—are famous for making water bead up and roll away.
They are used in products ranging from self-cleaning fabrics to industrial equipment.
However, these coatings have a major weakness: hot water. Once water reaches about 40 degrees Celsius, many of these surfaces stop working.
Instead of sliding off, hot droplets stick, spread, and leave behind residue.
Engineers at Rice University have now developed a simple and low-cost solution that keeps surfaces water-repellent even when liquids are nearly boiling.
Their new design can repel water at temperatures as high as 90 degrees Celsius, far beyond what traditional coatings can handle.
The breakthrough came from rethinking the problem. Most past research focused on changing the chemistry or texture of the surface itself.
The Rice team instead looked at how heat moves between a hot droplet and the surface it lands on.
Normally, superhydrophobic coatings rely on tiny microscopic textures that trap air, creating a cushion that prevents water from touching the surface directly. This air layer reduces sticking and allows droplets to roll off easily.
When a hot droplet lands on a cooler surface, however, part of the droplet evaporates and then condenses inside those tiny textures. The trapped air is replaced by liquid bridges that glue the droplet in place. This is why hot liquids cling even to surfaces designed to repel water.
To stop this process, the researchers created what they call a multilayered insulated superhydrophobic coating.
It consists of a thin insulating layer—similar to spray foam—placed underneath a standard water-repellent coating. The insulation slows the heat transfer from the droplet into the surface, reducing evaporation and condensation inside the texture. With fewer liquid bridges forming, the droplet remains on the air cushion and continues to slide away.
Tests showed that the new coating stayed slippery even as temperatures rose. In experiments where heated droplets were placed on tilted surfaces, traditional coatings became sticky, forcing droplets to grow larger before gravity could pull them off. The insulated surfaces, however, allowed droplets to roll away much sooner.
The researchers also simulated real-world conditions by blasting the surfaces with hot water jets and repeatedly striking them with hot droplets for days. Standard coatings failed quickly, while the insulated versions continued to repel water for much longer. In another test, hot liquids such as milk, coffee, and soup left almost no residue on the new surfaces compared with heavy buildup on conventional coatings.
Because the method uses inexpensive, widely available materials and simple spray techniques, it could be scaled up for industrial use without the high costs associated with advanced nanotechnology manufacturing. Potential applications include food processing, medical sterilization, chemical production, and desalination—any industry where equipment regularly encounters hot liquids.
The researchers say further improvements will focus on making the outer coating more durable so it can withstand harsh environments over long periods. Even so, the concept has already demonstrated that controlling heat flow can dramatically improve performance.
By preventing hot liquids from sticking, this technology could reduce contamination, simplify cleaning, and improve efficiency across many industries.
The study shows that sometimes the key to solving a long-standing problem is not changing the surface itself, but changing how heat moves through it.
