In this dataset, it is a filing that combines a phase-change material or latent heat storage claim with a claim aimed at improving how fast heat transfers into or out of that material — typically through conductivity enhancement, charge-rate improvement, or heat-transfer geometry. The search deliberately pairs storage-material claims with rate-of-transfer claims because storage capacity alone is rarely the commercial bottleneck; discharge speed usually is. This is why the dataset spans heat-exchanger hardware (F28D, F28F), materials science (C09K) and application-specific integration into batteries, electronics and solar collectors rather than sitting in a single IPC class.

Filing activity in this corpus is spread across corporate, institutional and individual-inventor assignees rather than concentrated in one dominant player, and co-filing between assignees is uncommon — only four co-assignee pairs appear across 391 families. Several previously active filers, including General Electric and multiple research institutes, show zero filings in the most recent tracked year. That pattern suggests a field with a long tail of contributors rather than one or two companies controlling the core intellectual property.

Filings rose steadily from 29 in 2017 to a peak of 45 in 2023 before flattening, with the 2026 count (12, partial year) tracking well below the peak. That shape is typical of a field where the core mechanical and materials approaches to conductivity enhancement have become reasonably well established, so new filings increasingly target application-specific integration rather than fundamental mechanism claims. Note that publication lags filing by roughly 18 months, so the most recent one to two years in any trend chart will always look lower than they will once all filings publish.

The United States leads with 130 records in this dataset, followed by India at 67, the European Patent Office at 61, and WIPO PCT filings at 55, with Germany and Canada trailing at 13 and 11 respectively. The presence of a substantial WIPO PCT count alongside strong single-country filing in the US, India and Europe indicates that a meaningful share of applicants are pursuing multi-jurisdiction protection rather than filing in a single home market. A freedom-to-operate review limited to one office would miss most of the global claim picture here.

Relative to the dense heat-exchanger (F28D, F28F) and materials (C09K) clusters, several application-specific branches show thinner claim density, including hexagonal-packed tube array geometries, PCM integration for LED and electronics cooling, solar-thermal PCM hybrid collectors, and encapsulation designed specifically for battery pack thermal buffering. These are not unclaimed spaces, but they carry noticeably fewer filings than the core mechanism and materials clusters, making them worth a closer freedom-to-operate look before assuming they are blocked.