The Hidden Barrier to Wireless

When good glass goes bad, a Swiss startup finds a way through

Germany dreams of a digital future: smart cities, high-speed trains with seamless Wi-Fi, and 5G in every corner. But despite living in a world obsessed with innovation, the physical infrastructure around us — buildings, trains, and public spaces — remains out of sync with that vision. The network is evolving fast, yet the places we live and work in have not fully caught up. 

5G-Advanced is rolling out, Release-19 is locking down features right now, and 6G is being shaped at the International Telecommunication Union (ITU) under the IMT-2030 banner. In other words, the next wave is arriving as a careful evolution, not a hard reset. That’s great news for innovators across the stack. But it also exposes a quieter challenge: connectivity is not only about core networks, spectrum, or apps. Sometimes, the building itself becomes part of the connectivity problem — and increasingly, part of the solution. 

Signal Lost: When the Smart Building Turns Silent 

Inside buildings, the limiting factor is often physics, not features. The first place that physics bites is at the building envelope, where radio waves must pass from outside to inside. In most cases, that means through the glass. Modern façades are engineered for energy performance, not for radio transparency. Low-emissivity (low‑E) glass — now standard in nearly all new commercial buildings and trains — contains ultrathin metallic layers, often silver or tin oxide, designed to reflect heat. The effect on wireless is dramatic: recent wideband measurements report about recent wideband measurements report about 33.7 dB penetration loss at 6.75 GHz and 42.3 dB at 16.95 GHz, enough to erase most indoor signal advantage unless the façade is specifically engineered for radio entry. Even regulators underestimate this effect. Ofcom’s Connected Nations 2024 still assumes a generic 10 dB building-entry loss, while real-world tests in modern double-glazed offices measured 28–36 dB depending on angle of incidence. 

These coatings work wonders for heating bills but act like invisible mirrors for radio waves. Think of low‑E glass like a thermos: a reflective lining bounces energy back inside, reducing heat loss — but for wireless frequencies, that lining becomes a near-perfect shield. With buildings now optimized for insulation, we have inadvertently built energy-efficient Faraday cages. 

Ripping out these windows would make no sense environmentally or financially. Whole‑life‑carbon guidance favors retrofit‑first strategies that avoid the embodied carbon of replacement. That’s why startups are now stepping in to reconcile sustainability with connectivity. 

nu glass: Turning Windows from RF Blockers into RF Gateways 

Switzerland’s nu glass, born out of research at EPFL, approaches the problem not by fighting physics, but by tuning it. Their portable laser process micro‑etches invisible patterns directly into the metallic coatings of existing low‑E panes. The result: selectively transparent “frequency windows” that allow 4G and 5G signals to pass through without degrading the glass’s thermal performance. The process is carried out onsite, window by window, without removing the glazing. Each pane takes around fifteen minutes to complete, using micro‑lines roughly 25 μm wide — thinner than a human hair and invisible to the naked eye. 

The technology was first developed for trains. EPFL researchers originally sought to improve glazing insulation and reduce HVAC energy use, which accounts for roughly a third of a train’s total power. When a rail partner warned that the new high‑performance glass would block mobile signals, the idea of laser micro‑patterning was born. The solution maintained energy efficiency while restoring signal transparency. 

By 2025, nu glass had treated more than 20,000 windows across Europe. The company joined Deutsche Bahn’s Gigabit Train initiative, conducting summer trials in DB’s TrainLab alongside Ericsson, Telefónica, Vantage Towers, and Icomera. In France, SNCF Voyageurs and Île‑de‑France Mobilités began retrofitting commuter trains on Transilien Line N, after years of customer complaints about mobile dead zones. Early results show significant improvements in passenger connectivity without compromising energy efficiency or window lifespan. The system is passive, requires no maintenance, and cuts roughly 28 MWh of electricity per train per year — about the annual consumption of twenty people. 

If laser‑tuned glass can unlock trains, imagine what it could do for offices, hospitals, and schools — buildings where heritage restrictions and cost constraints make full replacements unrealistic. Retrofit solutions like this could turn energy‑saving windows into RF gateways, allowing existing networks to finally reach the people, sensors, and devices trapped behind insulated glass. 

Beyond Trains: Making Buildings Radio‑Ready 

Startups are expanding this idea beyond transportation. In Japan, AGC Glass developed WAVETHRU, a laser‑patterning retrofit that restores up to 25 dB of signal strength in energy‑efficient glazing. The company also introduced WAVE ANTENNA, a transparent glass‑integrated antenna developed in collaboration with telecom operators. It embeds radiating elements directly into the window, turning façades into active components of the mobile network. Similarly, Canada‑based ALCAN Systems created transparent antenna films that can be laminated into glass or wall panels, enabling adaptive 5G and 6G coverage inside buildings without visible hardware. 

Each of these technologies reflects the same mindset: rethinking the physical environment as part of the wireless ecosystem. Instead of adding more base stations, these startups make the built world itself more permeable to mobile signals. 

Slices vs. Windows: Why Building Physics Shapes the Network

For enterprises deploying private 5G or campus networks, this lesson is crucial. Network slicing and advanced radio features promise flexible performance, but none of it matters if the signal never makes it to the devices inside. In many cases, companies lease public‑operator infrastructure, giving them little control over antenna placement or building penetration. As a result, even the most advanced slice can be crippled by physical barriers — especially in buildings wrapped in thermally efficient glass. However, a parallel path is emerging through private 5G networks such as those offered by startups like Berlin based airpuls, which deploy affordable, in-building coverage using small cells. These systems deliver maximum signal availability exactly where it’s needed — offices, production floors, and logistics hubs — and represent a practical alternative to network slicing models. In such cases, comprehensive indoor coverage becomes part of the managed service itself, making glass retrofits unnecessary for achieving strong, reliable connectivity. 

However, if retrofits are inevitable, material‑aware solutions like nu glass, WAVETHRU, and ALCAN’s antenna films provide retrofit‑ready fixes that improve performance without structural overhaul. They transform the envelope from an obstacle into an opportunity — a principle that could soon become standard as frequencies climb toward upper mid‑band and sub‑THz ranges, where even minor materials differences matter. 

The Glass Barrier to Connectivity - And the Startups Breaking Through 

Sometimes innovation doesn’t mean adding something new; it means revealing what’s already there. The walls and windows around us aren’t just barriers; they are the next frontier of connectivity design. As 5G‑Advanced expands and 6G takes shape, the challenge is no longer just software or spectrum — it’s about making sure the physical world is ready to let those signals in. 

Startups are leading that charge. By combining materials science, sustainability, and radio engineering, they show that the future of wireless won’t be built only in code or silicon, but etched into the surfaces that surround us. When good glass goes bad, innovation finds a way through.