By: Yimeng Pan, Founder, TheraSun
How Yimeng Pan’s product vision and Xiang Li’s materials engineering challenged decades of conventional thinking and gave rise to TheraSun.
Stand in any parking lot in America and look at the cars. Half the windows are tinted, and every one of those tints was sold on the same pitch: darker, cooler, done.
Yimeng Pan looked at the same windows and saw a question nobody was asking.
The Question from Florida
When Pan was living in Florida, she learned something most people never think about. UVA, the ultraviolet rays most associated with premature skin aging, can pass through ordinary glass.
The science wasn’t new. What struck her was the contradiction around it. People remembered sunscreen before stepping outside. But once inside a car, an office, or their own home, they assumed the glass around them was enough protection for their skin.
Rather than jumping directly into product development, Pan spent months speaking with automotive installers, drivers, homeowners and commercial customers across different markets. She found that nearly every conversation revolved around the same trade-off. Reducing heat usually meant accepting darker interiors, while preserving daylight often meant sacrificing solar protection.
“Sunlight isn’t a single thing,” Pan says. “It’s ultraviolet, it’s blue light, it’s red light, it’s infrared heat, all in one, each with different effects. If only certain parts are harmful, why should we sacrifice everything else?”
She stopped seeing glass as a barrier and started seeing it as an interface, one that could shape how people experience light. The challenge wasn’t to block daylight. It was to understand it well enough to manage it. What if the problem was never sunlight?
Light, Curated
That question became TheraSun, the New York advanced-materials startup Pan co-founded, and its answer is a window film that works less like sunglasses and more like an equalizer.
Long before the chemistry was finalized, Pan defined what the product needed to accomplish from a user’s perspective: preserve the parts of daylight people enjoy, filter out the parts they don’t, and do so without making spaces feel darker. That product vision became the foundation for a close collaboration with co-founder Xiang Li, whose expertise in materials science helped transform those ideas into manufacturable technology.
The glass stays clear, and the cabin stays bright. But invisibly, the film is making choices, throwing out UV, dialing down harsh blue light, and purposefully letting through the warm red light, the part of daylight that makes a space feel good. The founders call the category they’re building “daylight management.” They describe it simply: “Just daylight, curated for you.”
Turning that idea into a scalable product, however, would take more than a vision. It would take an engineer who was just as fascinated by the challenge as Pan was.
A Livestream, a Message, a Partnership
Pan and TheraSun co-founder Xiang Li met in an unexpectedly ordinary way. After moving to New York, Pan shared an apartment with a roommate who liked to livestream while cooking. The format was simple. While her roommate was making dinner, Pan would talk about entrepreneurship, product ideas, and the less glamorous work that goes into building a company.
Among the viewers was a chemical engineering graduate from Georgia Tech named Xiang Li. He wasn’t looking for a startup. He was looking for advice. One evening after a livestream ended, he sent Pan a message asking about coffee chats and breaking into the startup world.
They stayed in touch, exchanging ideas from their respective worlds. Pan shared the product concepts she couldn’t stop thinking about, while Li shared what he was learning in research labs. So when Pan began exploring whether sunlight could be managed rather than simply blocked, Li was the first person she called. “I remember being fascinated by the challenge,” Li recalls. “It wasn’t an easy one, but it asked us to rethink a long-standing assumption in materials design.”
Pan understood what people needed from the product, while Li understood what the material would have to do to deliver it. Their complementary perspectives made them natural partners.
Brutal to Build
Long before he began working on windows, Li was already fascinated by a simple question. How can a material let some things through while keeping others out? At Georgia Tech, he focused on membrane science, the field devoted to materials that let some things pass and stop others. Water through, salt out. Oxygen through, nitrogen out.
Window film, he realized, was the same puzzle wearing different clothes. Instead of separating molecules, separate light. Easy to say. Brutal to build. The film has to stay clear enough to see through, reject heat, kill UV, and carry a faint warmth in its color, all at once, on a real production line, at a price the market will pay.
The trick happens at the nanoscale. TheraSun’s film embeds engineered nanoparticles between ultra-thin polyester layers, each particle sized and tuned to sort daylight by wavelength, absorbing some, passing others. The physics is unforgiving. The same nanoparticles that shape the light’s warmth also scatter it, so every step toward the right spectrum risks a step away from clarity. Holding onto both at once is the balancing act TheraSun set out to solve.
“The easy version of this product doesn’t exist,” Li says. “If it did, someone would already be selling it.”
TheraSun began by working backward from the experience Pan wanted to create: a brighter, more comfortable cabin on long drives and workspaces filled with daylight but less UV exposure. Li then translated those goals into proprietary formulations and scalable coating processes. That work now forms part of the company’s growing intellectual property portfolio, while the underlying chemistry remains closely guarded throughout manufacturing. “Engineering is often about accepting compromises,” Li says. “Our challenge was deciding which compromises we refused to make.”
TheraSun’s founders made an early decision. The product would be judged by measurable performance, not sweeping wellness claims. Pan and Li spoke with installers, distributors, architects, and end users to understand what the market valued and how professionals evaluated window film. Pan translated those insights into a clearer product and category strategy; Li turned them into testable optical targets, including visible-light transmission, infrared rejection, and UV rejection. “The product has to earn trust on numbers you can verify and on how a space actually feels,” Li says.
More Than Window Film
Today TheraSun sells through tint shops and automotive installers, with a product line that runs from its flagship spectral-selective ceramic film to switchable smart film that flips from clear to private at the touch of a button. The next chapter is buildings, offices, schools and glass facades, where Li’s LEED credential from the U.S. Green Building Council comes into play and where daylight quality is becoming a design requirement instead of an afterthought. “Products evolve. Applications evolve,” Pan says. “But the problem worth solving shouldn’t.”
For Pan, window film is only the first application. The larger goal is to rethink how advanced materials can improve the relationship between people and the environments they live in. That broader vision has also prompted conversations beyond the window-film industry.
In discussions with researchers in membrane materials and spectral engineering, Pan and Li explored how the same spectrum-management principles could be applied to agricultural films for greenhouses and other controlled growing environments. Such films could help crops receive more of the light they use for photosynthesis while limiting unwanted heat, creating a more favorable growing environment.
For Pan and Li, those conversations reinforced a belief at the heart of TheraSun. They were building not just a better window film, but an advanced-materials platform. Not darker windows. Better daylight. It may sound like a small distinction, but it reflects an entirely different way of thinking about light, and it all goes back to the question Pan first asked while living in Florida. What if the problem was never sunlight?
This article is based on interviews with TheraSun co-founders Jasmine Pan and Jimmy Li.
