Fall 2025
By Katharine Shilcutt

Juan José Castellón landed in Houston straight from the Venice Biennale, where global visions of the future spilled across galleries and pavilions. He arrived not just with jet lag but with a warning — and a challenge.

“We don’t yet know what’s coming,” he told the crowd at Rice’s Carbon Hub annual conference May 12. “And that’s a problem.” The celebrated architect and Rice professor wasn’t just talking about materials science. He was talking about meaning.

In a room full of engineers, industrialists and carbon wonks, Castellón stood out on a conference panel dedicated to “Introducing Advanced Materials Into Applications” — part philosopher, part provocateur. “Ask a brick what it likes,” he said, invoking architect Louis Kahn. “It will say: ‘I like an arch.’” Then he smiled. “So the question is — what do our new materials like? And how can we listen?”

Castellón was there to talk about carbon nanotubes — those ultralight, ultra-strong carbon structures with near-mythic properties. They’re 100 times stronger than steel, more conductive than copper and thin as a virus. But for Castellón, the promise of CNTs wasn’t just mechanical. It was societal.

“We have to understand what the world needs,” he said. “What does sustainability mean? How can we build better? How can we connect? How can we integrate science and society in a meaningful way?”

Castellón, co-founder of xmade — an architectural firm based in Basel, Switzerland, and Barcelona, Spain — and a rising voice in sustainable design, is partnering with DexMat, a CNT-based materials startup spun out of Rice, to explore how these miraculous fibers can transform architecture. Not just as a gimmick, but as a gesture. An answer. A conversation starter.

“When you see something built beautifully with less — something that performs but also inspires — you don’t need an instruction manual,” he said. “You feel it. It makes the future tangible.”
 

We have to understand what the world needs. What does sustainability mean? How can we build better? How can we connect? How can we integrate science and society in a meaningful way?

Others on the panel emphasized production scale, market disruption and grid infrastructure, and Castellón pulled the conversation toward purpose. “This isn’t just about performance. It’s about value,” he said. “Not monetary value — but what something means to the people who use it, live with it, build it.”

It wasn’t an abstract appeal. DexMat’s CEO Bryan Guido Hassin followed with real-world stakes: copper is expensive, toxic to extract and geopolitically messy. CNTs, by contrast, are made from abundant feedstocks and offer exponential gains in strength-to-weight ratio. “We’re solving real pain points,” Hassin said. “And yes, we want the tech to scale. But it has to matter, too.”

F1 engineer Claudio Santoni, engineering director for Aston Martin, chimed in from the world of elite motorsports, where milliseconds matter more than margins. “We don’t patent — we just move fast,” he said, recounting how carbon fiber monocoques were smuggled into racing in the 1980s. Today, Santoni is collaborating with SABIC and Aramco to test CNT-based battery casings and components. “It’s not just a science problem. It’s a timing problem. It’s a design problem.”

And for Dhaval Shah, general manager for corporate technology and innovation at SABIC, the problem is also one of alignment — between producers, designers, policymakers and educators. But that’s exactly where Castellón wants to live.

“We need a mindset that starts in our universities but moves out into the world,” he said. “That includes citizens, students, institutions. People. What do they need? How can we offer that? How do we build with less, but better?”

If you ask a CNT what it likes, it probably doesn’t say much yet. But if you weave it into a cable net structure, a fibrous canopy or a cathedral of tensile possibility — maybe it speaks after all.
 

The 411 on CNTs

CNTs are like rebar for the 21st century — only smarter, lighter and ready to transform everything from the power grid to public libraries. They offer a lower environmental cost than mining metals like copper and are made from hydrocarbon feedstocks, including natural gas and even plastic waste. And CNTs can support a circular carbon economy by turning emissions into materials.

Size: About 50,000 times thinner than a human hair

Structure: Cylindrical tubes made of a single layer of carbon atoms

Strength: Up to 100 times stronger than steel by weight

Conductivity: More conductive than copper

Weight: Extremely light-weight and flexible

Why architects and engineers love them:

• Tensile strength: Enables ultralight structures that resist tension and bending
• Electrical conductivity: Can replace traditional copper wiring in smart buildings, aerospace and even electric vehicles
• Thermal conductivity: Dissipates heat efficiently, critical for electronics and extreme environments
• Low density: Ideal for lightweight construction and mobility applications

CNTs are already in development for:

• Submarine power cables
• Battery casings for EVs
• Lightweight wiring in satellites and aircraft
• Architectural tension structures and design prototypes

Building With Less
Juan José Castellón’s Vision for Future Cities

Castellón has been inspired by the possibilities presented by CNTs, but first he needed to understand exactly how they work. The first step was to test the capacity to fabricate with robots, and now he’s trying to understand the structural performance of the fibers. Next, he said, will be incorporating conductivity to find ways to integrate other potential uses, such as harvesting energy or lighting. “I’m focusing on this material because I can envision where it will lead to — to a new paradigm — and I’m trying to follow in this direction,” he told the crowd at the Carbon Hub annual conference. “This is the material that, to me, has many answers to my questions.”

Nature-inspired design: Castellón draws from spiderwebs and other natural systems to create ultralight structures that use minimal material while maximizing performance.

Carbon fiber innovation: Working with CNT fibers, his team prototypes woven structural components that are lightweight, strong and potentially conductive — opening doors to energy-harvesting buildings.

Robotic fabrication meets architecture: No more manual cable-tightening. Robotic systems now help spin intricate netlike facades that can respond to sunlight and temperature, adjusting to the environment in real time.

Reimagining the building skin: Forget static glass. Castellón’s cable-net prototypes offer a breathable, adaptive alternative to traditional facades, promising better energy performance and dynamic aesthetics.

From ceramics to carbon futures: Merging Barcelona’s ceramic traditions with futuristic materials, his modular rooftop systems collect rainwater, provide shade and could transform urban skylines.

Paradigm shift: Castellón’s ultimate aim? A new material culture that connects structure, sustainability and beauty — one thread at a time.