This landscape only includes families that combine molded fiber, moulded pulp or moulded fibre packaging terminology with specific durability language — wet strength, compression strength, drop resistance or stacking durability — inside the D21H, D21J or B65D65/38 classification. A general moulded-pulp forming patent that never claims a durability property is excluded, as is a generic packaging patent that never references the fiber substrate. That narrows the set to 35 families, so absolute counts are small and should be read as a focused slice rather than the full moulded-pulp packaging field.

The trend data shows six filings in 2019, the highest single year in the 2015-2026 window, with the 2022 midpoint back down to zero and no clear recovery since. This pattern is more typical of a short filing burst around a specific claim opportunity — likely the core wet-strength and compression-strength combinations — than of a steadily growing field. Publication lag of roughly 18 months means the very last one to two years will always look artificially quiet, so some of the recent flatness may still resolve upward as pending filings publish.

The recent-momentum data tracks a mix of a specialist moulded-fibre technology firm, a Singapore-based packaging company, and larger consumer-goods multinationals, but every one of them shows zero filings in the latest tracked year. There is no single assignee with sustained, repeat recent activity in this specific durability-claim niche. Co-assignee pairings are also few and mostly link named individuals rather than corporate teams, suggesting the field is currently driven by dispersed, smaller-scale filers rather than one dominant incumbent.

US5034097A, assigned to Georgia-Pacific Resins and granted in 1991, claims a composition combining epoxidized polyamide wet strength resin with lecithin that improves both wet strength and internal bonding in paper and molded pulp products. It remains among the most-cited records in this landscape decades after grant, which signals it is still treated as a reference point for wet-strength resin chemistry. It does not block wet-strength approaches generally — only the specific epoxidized-polyamide-plus-lecithin composition and closely equivalent formulations — so resin systems built on different chemistries, such as bio-based alternatives, sit outside its claim scope.

The IPC composition shows structural and forming claims (D21J, covering 23 of 35 records) far outweigh additive-chemistry claims (C08L, C08G and C08K, each appearing only a handful of times). That imbalance suggests durability improvements built around fibre-polymer additive blends, non-lecithin bio-based wet-strength systems, or stacking-durability test/claim methods are comparatively under-claimed relative to the well-covered forming-geometry approaches. Any new filing in these areas should still be checked against the older, highly-cited manufacturing and resin-chemistry baseline patents in this set, since some of that art predates 2015 and would not otherwise surface in a narrow date-bounded search.