The Physics and Patent Logic of Passive Radiative Cooling
Passive radiative cooling (PRC) dissipates heat by emitting infrared radiation through Earth’s atmospheric transparency windows — primarily 8–13 µm, with a secondary window at 16–28 µm — directly into cold outer space, requiring no electricity input. An effective PRC structure must accomplish two simultaneous spectral tasks: reflect nearly all incident solar radiation (0.3–2.5 µm) to avoid solar heat gain, and emit thermal radiation at high emissivity within the atmospheric window to maximise radiative heat loss.
This dual spectral requirement — high solar reflectance plus high mid-IR emissivity — is the central engineering challenge that has driven patent activity across four distinct material and structural approaches. The atmospheric window physics is consistently cited across assignees and jurisdictions: Korea University Research and Business Foundation describes mid-infrared absorbing and emitting layers tuned to the sky window, while Palo Alto Research Center (PARC) quantifies the 8–13 µm and 16–28 µm windows as design targets for metamaterial emitters.
The atmospheric transparency window is the spectral band (primarily 8–13 µm, with a secondary window at 16–28 µm) through which blackbody radiation from Earth’s surface escapes to space without being absorbed by atmospheric gases. Passive radiative cooling structures are engineered to emit intensely within this band, effectively using outer space as a heat sink.
Passive radiative cooling (PRC) is a zero-energy thermal management approach that dissipates heat by emitting infrared radiation through Earth’s atmospheric transparency windows (8–13 µm) directly into cold outer space, requiring no electricity input.
From Lab Breakthrough to Commercial Filing: The Innovation Timeline
The earliest relevant PRC filing in this dataset is from Stanford University (2015, US), which introduced solar-spectrum-reflecting photonic structures enabling simultaneous solar rejection and mid-IR emission — representing the foundational daytime passive cooling breakthrough. The decade that followed shows a clear three-wave structure: foundational materials IP, system integration, and now bifunctional energy harvesting.
The 2016–2019 cluster saw PARC file core metamaterial nanopore emitter patents in the US (2016) and Japan (2017, 2019), establishing modular scalable dry-cooling systems. Fujifilm filed vacuum-insulated far-infrared radiator devices in Japan (2019), and Columbia University articulated the polymer/metal reflective stack architecture via a Chinese filing in 2018. The 2020–2022 cluster brought Korea University Research and Business Foundation into EP and KR with multilayer photonic stacks, and the University of Colorado filed polymer-based selective radiative cooling structures (priority approximately 2020).
“The most recent filings signal a paradigm shift: PRC is no longer positioned solely as a cooling load reducer but as an energy harvesting technology.”
The 2023–2026 frontier period is the most active in the dataset, with filings from Penn State Research Foundation (simultaneous daytime cooling and photovoltaic power generation, WO 2025), the University of California (Radiative Cooling Engine using a modified Stirling engine, WO 2026), AGC Glass Europe (glass-silver reflective substrate with a fluid heat exchanger, WO 2025), and Shenzhen University (building-level PRC potential assessment methodology, CN 2025).
Map the full passive radiative cooling patent landscape — including assignee clusters and white-space analysis — in PatSnap Eureka.
Explore Patent Data in PatSnap Eureka →Four Technology Clusters Defining the IP Landscape
The passive radiative cooling patent dataset organises into four technically distinct clusters, each with different material systems, fabrication routes, and performance trade-offs. Understanding which cluster a given filing belongs to is essential for freedom-to-operate analysis and white-space identification.
Cluster 1: Metamaterial Nanostructured Emitters
This approach, led by Palo Alto Research Center Incorporated with 4 filings across US, JP, and KR, uses metal-plated tapered nanopores fabricated via modified anodic aluminum oxide (AAO) self-assembly and electroless plating to create an “ultra-black” emitter with emissivity approaching unity within atmospheric windows. A distributed Bragg reflector sits above the emitter to reflect solar radiation while passing emitted infrared energy. The conduit structure allows liquid coolant to flow against the reverse face of the emitter metal sheet, enabling dry cooling of industrial systems at scale. PARC’s foundational AAO/metamaterial patents — all currently active — form a blocking position on tapered nanopore ultra-black emitters at scale.
Cluster 2: Polymer and Particle Composite Films
Polymer matrices — typically fluoropolymers, PDMS, or polyethylene — loaded with inorganic particles (TiO₂, SiO₂, CaCO₃, SiC, ZnO, Al₂O₃) achieve spectrally selective emission through particle-induced infrared absorption and emission. These films are designed to be flexible, low-cost, and scalable to large areas. Key assignees include the Hong Kong Polytechnic University (smart sub-ambient coating with TiO₂, SiO₂, and fluorescent particles, WO 2021), the University of Colorado (polymer-based selective radiative cooling structures, SA 2023), and independent inventor Fain, Romy M. (flexible film PRC structures, EP 2024 and JP 2025). According to WIPO, PCT filings in materials and coatings for thermal management have grown consistently over the past decade, reflecting the commercial pull for scalable surface treatments.
Polymer and particle composite PRC films — using matrices such as fluoropolymers loaded with TiO₂, SiO₂, CaCO₃, SiC, ZnO, or Al₂O₃ — are designed to be flexible, low-cost, and scalable to large areas, making them candidates for building facades, textiles, and solar panels.
Cluster 3: Photonic Multilayer Stacks
This approach stacks alternating dielectric layers — such as HfO₂/SiO₂ photonic crystals or polymer/inorganic bilayers — to engineer spectrally selective optical properties: near-total solar reflection and high infrared emissivity in the atmospheric window. Korea University Research and Business Foundation dominates this cluster with 5 filings across EP and KR (2021–2023), featuring devices with a reflective metal layer on a substrate topped by an uneven-patterned first radiation layer and a second radiation layer with differing refractive index, producing selective mid-IR emission. Stanford University’s 2015 US filing is the foundational photonic stack patent in the dataset. Research published in Nature has validated sub-ambient daytime cooling using photonic multilayer approaches, underpinning the academic IP activity.
Cluster 4: Vacuum-Insulated Far-Infrared Radiator Devices
Fujifilm Corporation’s architecture (2 JP filings, 2019) encloses the cooled object in a vacuum-insulated container at ≤10 Pa with an opening sealed by a far-infrared transparent window. A far-infrared radiator with emissivity ≥0.80 in the 8–13 µm band is in thermal contact with the object and emits through the window while remaining thermally isolated from the warm exterior. This approach minimises the parasitic conductive heat gains that degrade performance in open-surface designs — a critical advantage in high-precision cooling applications.
PARC’s foundational AAO/metamaterial patents across US, JP, and KR are all currently active and form a blocking position on tapered nanopore ultra-black emitters at scale. Any industrial dry-cooling system using this architecture will require a licensing assessment or design-around using alternative nanostructure fabrication routes.
Application Domains: Buildings, Data Centres, and Beyond
Passive radiative cooling patent filings address at least six distinct application domains, each with different performance requirements, integration challenges, and market entry points. The breadth of applications — from urban-scale building assessments to portable refrigeration — reflects the technology’s versatility as a zero-energy thermal management platform.
Building Cooling and Urban Heat Island Mitigation
The largest application cluster in this dataset targets building energy efficiency. Shenzhen University’s 2025 CN filing develops a computational framework to assess PRC potential across entire urban building stocks using 3D building models, meteorological data, and radiative cooling material performance data. Columbia University’s polymer/reflector stack system explicitly targets building cooling during peak demand to reduce grid stress. The Hong Kong Polytechnic University’s smart coating targets building surfaces in hot climates. As noted by the IEA, space cooling already accounts for a significant and growing share of global electricity demand, making zero-energy alternatives like PRC increasingly strategically important.
Data Centre and Server Thermal Management
Two 2024 CN filings from Suzhou Yuannao Intelligent Technology Co., Ltd. describe server heat dissipation systems integrating a radiative cooling module (emitting through the 8–13 µm atmospheric window) with phase-change energy storage and a coolant distribution unit. When ambient temperature is sufficiently low, the radiative cooling module alone satisfies server heat rejection needs, switching to conventional cooling only when outdoor conditions are unfavourable. This architecture directly addresses hyperscale data centre power use effectiveness (PUE) challenges.
Two 2024 CN patents from Suzhou Yuannao Intelligent Technology Co., Ltd. describe server heat dissipation systems that integrate a radiative cooling module emitting through the 8–13 µm atmospheric window with phase-change energy storage and a coolant distribution unit, targeting hyperscale data centre PUE improvements.
Photovoltaics and Hybrid Energy Systems
Penn State Research Foundation’s 2025 WO filing integrates a PRC layer over a solar cell to simultaneously reduce cell operating temperature and generate photovoltaic power from the same aperture. The PRC film is visibly transparent and IR-opaque, passing sunlight to the cell while emitting thermal radiation to space. Fain’s EP (2024) and JP (2025) patents cover transparent PRC films applied directly over solar cell panels and over enclosures containing active cooling units.
Ground-Source Heat Pump Augmentation
Shandong Zhongrui New Energy Technology Co., Ltd.’s 2014 CN patent integrates a passive space radiative cooler with a ground-source heat pump to address seasonal thermal imbalance in the soil. The PRC unit operates at night to reject accumulated heat to space, restoring the soil temperature gradient that the heat pump depends on — one of the earliest system-integration filings in the dataset.
Refrigeration and Cold Chain
The TEC–PRC hybrid device from the University of Science and Technology of China (CN, 2020) couples a thermoelectric cooler with a sky radiative cooling body to increase composite refrigeration capacity to over 1,000 W/m², targeting portable refrigeration applications. The flat-panel space radiative cooler with air flow channels from Zhejiang Yaofu Energy Management Co., Ltd. (CN, 2019) addresses scalable low-cost radiative refrigeration for everyday use.
Conducting freedom-to-operate analysis in passive radiative cooling? PatSnap Eureka surfaces blocking patents and white spaces across all jurisdictions.
Run FTO Analysis in PatSnap Eureka →Geographic and Assignee Patterns in the Patent Dataset
Within this dataset, PRC-relevant filings span at least 8 jurisdictions, with distinct specialisation patterns: US and Korean entities dominate structural and material IP, while Chinese assignees lead in system-level integration and application-specific deployment. This geographic divergence has direct implications for market entry strategy and IP risk management.
US entities (PARC, Stanford) concentrated foundational IP in metamaterial emitters and photonic multilayer stacks early in the cycle. Korean entities (Korea University) built a strong multilayer photonic stack position across EP and KR. Chinese applicants account for the broadest range of application-specific deployments — buildings, servers, heat pumps, refrigeration, and ceramics — often through system-level claims that integrate PRC emitters with other thermal or energy components. Competitors entering the Chinese market should conduct freedom-to-operate analysis across these fragmented but numerous CN filings, as noted in guidance from EPO on navigating dense application-specific patent clusters.
Within the passive radiative cooling patent dataset spanning 2014–2026, US and Korean entities dominate structural and material IP, while Chinese assignees lead in system-level integration and application-specific deployment across buildings, servers, heat pumps, refrigeration, and ceramics.
Emerging Directions: Power Generation, Ceramics, and Urban Scale
The most recent filings (2024–2026) in this dataset signal five convergent directions that are redefining the scope of passive radiative cooling from a niche thermal management technique to a broader energy and infrastructure technology platform.
1. Simultaneous Cooling and Power Generation
Penn State Research Foundation’s 2025 WO patent and the University of California’s 2026 WO Radiative Cooling Engine patent represent a paradigm shift. The University of California filing introduces a modified low-temperature differential Stirling engine that converts the temperature difference between Earth’s surface and the cold night sky into mechanical and electrical work, enabling power generation during nighttime when solar photovoltaics are idle. This bifunctional approach could unlock new value propositions in off-grid and renewable energy systems.
2. Glass and Transparent Substrate Integration
AGC Glass Europe’s 2025 WO patent integrates a silver-reflective glass substrate (≥700 mg/m² Ag) with a convective heat exchanger loop, demonstrating that conventional glazing manufacturers are entering the PRC space for building envelope applications. This signals a potential shift from specialist materials companies to established construction materials players.
3. Building-Scale Computational PRC Assessment
Shenzhen University’s 2025 CN filing introduces 3D urban modelling combined with sky view factor calculations and Python-based net cooling power algorithms to quantify PRC potential at city scale — a prerequisite for large-scale urban deployment policy and product specification. This computational layer is a necessary precursor to building-code integration and urban-scale procurement decisions.
4. Server and Edge Computing Thermal Management
Two 2024 CN filings from Suzhou Yuannao embed PRC modules within liquid-cooled server architectures with automated switching logic, directly addressing hyperscale data centre power use effectiveness challenges. This represents the first clear evidence in this dataset of PRC technology being engineered specifically for the data centre market.
5. Advanced Ceramics for Daytime PRC
The Hong Kong University of Science and Technology’s 2024 CN filing on ceramic composite radiative cooling materials targets ultra-high solar reflectance (greater than 95%) combined with high infrared emissivity and mechanical strength, signalling a move beyond polymer films toward durable structural materials for outdoor deployment. This addresses a key durability limitation of current polymer-based approaches, which are subject to UV degradation and mechanical wear in outdoor environments. Standards bodies such as ISO are beginning to develop testing frameworks for radiative cooling materials, which will accelerate commercial adoption once durability benchmarks are formalised.
“Flexible film and transparent coating formats are underexploited commercially — multiple university assignees have filed, but no major manufacturer has consolidated this IP.”
Taken together, these five directions suggest that near-term product roadmaps should plan for bifunctional devices combining cooling with power generation, and that R&D teams should target system-level claims combining radiative emitters with energy conversion or storage modules — the clearest IP white space identified in this landscape. Energy storage and power electronics companies should monitor the convergence of PRC with nighttime power generation and daytime PV integration as potential adjacent disruption to conventional solar-thermal and battery-backup systems. For a deeper exploration of the patent data underlying these trends, PatSnap Eureka provides full-text search, citation mapping, and assignee clustering across the global PRC patent corpus.