Collaboration with COPV Manufacturers

Flexyshell is now seeking feasibility-stage collaboration with established pressure vessel and composite manufacturing companies.
The aim is to validate the structural and economic advantages of the Flexyshell architecture using existing test and production infrastructure.

Such partnerships can be structured as funded feasibility or co-development programs under NDA and option-to-license terms. This approach allows manufacturers to evaluate the concept at low risk while retaining the opportunity for priority access or exclusivity in later commercialization stages.

Why the Traditional Pressure Vessel Approach Has Limits

Hydrogen storage has long relied on a single structural concept — the rigid-walled pressure vessel.
Composite overwrapped pressure vessels, or COPVs, have been refined over decades and are widely regarded as the current state of the art.

Yet, despite advances in stronger fibers, smarter winding patterns, and improved resins, they remain bound to the same fundamental assumption: the wall itself must resist all internal pressure through rigidity.

This reliance on rigidity creates inherent structural conflicts. In COPVs, the same wall must simultaneously carry hoop stress, axial stress, and resist bending or local imperfections. Each additional load path introduces stress concentrations, making the vessel highly sensitive to minor defects or uneven geometry — conditions almost impossible to avoid in real-world applications.

The acronym “COPV” has become more familiar outside engineering circles recently — though unfortunately, not always for the right reasons. One certified COPV failed on a launch vehicle, leading to the dramatic loss of the Starship S36. Such events underscore a structural reality: rigid-wall vessels are fundamentally brittle, and their failure modes are abrupt and destructive.

On this page, we will show how Flexyshell overcomes these rigid-wall limitations. By allowing the cylindrical membrane to carry hoop tension while external tendons handle axial loads, Flexyshell decouples stress paths, enabling predictable, scalable, and inherently safer high-pressure storage — turning the internal pressure from a structural constraint into a stabilizing feature.

To see exactly how Flexyshell solves the problems inherent to rigid-wall COPVs, we’ve broken down the architecture and advantages into nine key aspects. Each section dives into a specific feature or benefit, from stress decoupling to modular scalability, providing a clear picture of why this approach is fundamentally different and safer:

  1. Multi-Axial Stress Conflict – How separating hoop and axial loads eliminates stress interactions that make rigid composites brittle.
  2. Brittleness and Crack Propagation – Why tension-dominated membranes tolerate local damage without catastrophic failure.
  3. Manufacturing and Quality Control Limits – How Flexyshell simplifies production and ensures repeatable performance.
  4. Recyclability and End-of-Life Impact – Turning high-pressure storage from disposable into maintainable and recyclable.
  5. Scaling and Cost Barriers – Why Flexyshell can grow in volume and pressure without the inefficiencies of thick COPV walls.
  6. Unpredictable Failure in COPVs – Contrasting COPV failure modes with the predictable mechanics of Flexyshell.
  7. Real-World Consequences and Chain-Reaction Risk – How integrated safety design prevents destructive cascades in multi-tank installations.
  8. Structural Integration and Modular Safety – The dual role of Flexyshell modules as both pressure vessels and structural elements.
  9. Scalable Architecture – How multiple cylindrical sections and standardized components enable on-site assembly of very long vessels, something impossible for traditional COPVs.

Each section is designed to be self-contained, so you can explore the features in any order — or follow them sequentially to understand the full system logic.

1. Multi-Axial Stress Conflict

In a COPV, the shell must simultaneously resist hoop, axial, and shear stresses. These load directions compete — especially near domed ends, bosses, and overwrap transitions. Each added load path introduces new stress concentrations that can trigger microcracks or delamination. The structure becomes highly efficient only under ideal internal pressure and uniform geometry — conditions rarely sustained in real service.

Any local imperfection, uneven cure, or impact instantly disturbs this balance — producing unpredictable local overstress.

By contrast, the Flexyshell architecture decouples these stresses. The membrane carries hoop tension only, while tendons take the axial loads. Each element works in a single, well-defined stress regime — eliminating the internal conflict that makes composite shells brittle and failure-prone.

2. Brittleness and Crack Propagation

COPVs rely on high-modulus fiber composites that behave elastically until failure, with virtually no ductility. Once a crack initiates — whether from manufacturing defects, UV degradation, or low-velocity impact — stress redistributes poorly. Local failure often cascades, causing catastrophic rupture.

Even small defects can compromise an entire tank.

A tension-dominated membrane system behaves differently. The membrane can redistribute load as it deforms — local yielding or wrinkling is benign and self-limiting. Because stresses act purely in tension, cracks or punctures do not trigger explosive failure. Local leaks are contained and repairable, rather than destructive.

3. Manufacturing and Quality Control Limits

COPVs depend on precise fiber placement, controlled curing, and flawless bonding between composite layers. Minor process deviations (voids, fiber waviness, resin-rich zones) severely weaken the structure. Full-scale testing and certification are expensive because every vessel is a unique composite laminate with inherent variability.

In contrast, the Flexyshell principle simplifies the structural role of each part. The pressure membrane can be made from high-quality films, textiles, or polymer liners produced by industrial processes with well-understood uniformity. Tendons and end dome systems are standardized, replaceable components with well-characterized properties. This separation of function makes manufacturing repeatable, inspectable, and certifiable without reliance on destructive qualification.

4. Recyclability and End-of-Life Impact

Another fundamental distinction lies in material circularity.
COPVs are multi-material laminates of carbon fiber, thermoset resin, and metallic liners — inseparable after curing. Once a COPV reaches end of life, it cannot be disassembled or recycled; most are destroyed or landfilled as hazardous waste.
In contrast, Flexyshell modules use thermoplastic membranes instead of thermoset composites, along with metallic or composite dome systems and independent tendons. Each element can be replaced, refurbished, or recycled individually, turning the storage system into a maintainable, fully recyclable asset rather than disposable equipment.

5. Scaling and Cost Barriers

Increasing the volume or pressure rating of a COPV requires proportionally thicker composite walls and more intricate winding patterns. Thicker walls exacerbate the stress gradient through the vessel, making material usage less efficient. As vessel size grows, structural weight increases faster than the additional gas it can contain, limiting COPVs to small- and medium-scale storage and making very large tanks impractical.

The tension-based design scales naturally. Since both pressure containment and structural stability rely on tensile members, scaling the vessel size mainly increases the number or length of tendons, not wall thickness. The result is a linear cost–strength relationship, unlocking practical large-volume hydrogen storage with lighter structures and lower embodied energy.

6. Unpredictable Failure in COPVs

Composite overwrapped pressure vessels (COPVs) were developed to overcome the weight penalty of steel tanks. However, their complex, heterogeneous structure — combining fibers, resin, and metallic liners — makes their behavior impossible to predict purely from calculations. Local flaws, fiber misalignment, and resin variability create stress concentrations and failure paths that cannot be modeled with full reliability. As a result, extensive destructive and non-destructive testing remains essential simply to define a safe operating envelope. This dependence on empirical validation, codified in ISO and UN testing standards, is not a procedural inconvenience but a fundamental limitation of filament-wound design.
COPVs fail through complex, non-linear modes — resin cracking, fiber-matrix debonding, delamination, and localized buckling. These processes are difficult to model or detect before failure, so sudden, catastrophic failure can occur without warning.
Even the most advanced COPV systems have shown that sudden failure remains an inherent risk. Two well-known examples — the explosion of SpaceX’s Falcon 9 during the 2016 Amos-6 launch preparations and the more recent loss of Starship Ship 36 during testing — were both triggered by high-pressure COPV tank failures. These incidents, despite occurring in systems built to aerospace standards and tested under extreme scrutiny, illustrate that COPVs can fail abruptly and without warning, releasing stored energy in an instant. They demonstrate that the brittleness and lack of benign failure paths are not theoretical weaknesses — they are practical limitations of rigid composite overwrap designs.

Flexyshell resolves this fundamental uncertainty at the structural level.
Instead of forcing a single composite shell to carry both hoop and axial stresses, the architecture separates them entirely: the flexible cylindrical membrane carries only hoop tension, while the external tendon network carries the axial and external loads. Each element operates in a single, well-defined stress regime — simple to analyze, easy to monitor, and predictable in failure.
Because no rigid matrix is required to lock fibers in place, Flexyshell eliminates the brittle thermoset layer that causes crack initiation in conventional COPVs. The use of flexible, high-strength polymers or thermoplastics allows local deformation or wrinkling without loss of integrity, transforming pressure from a destabilizing force into a stabilizing one.
As a result, local damage or membrane rupture leads only to a controlled pressure release rather than an explosion — the stored energy dissipates harmlessly instead of driving fragment acceleration.
This clear functional division enables reliable analytical modelling and greatly reduces dependence on destructive testing. Each component — membrane, tendon, or end dome system — can be validated and replaced independently, creating a modular, certifiable system whose performance can be demonstrated progressively rather than through single-use burst tests.
In short, Flexyshell replaces empirical uncertainty with mechanical transparency: a pressure vessel architecture that behaves exactly as its equations predict — tension where expected, pressure where needed, and no hidden failure paths in between.

In stationary hydrogen storage systems, COPVs are often arranged closely to maximize space efficiency. When one vessel fails catastrophically—due to internal defects or pressure-related damage—the resulting blast and debris can instantly compromise neighboring tanks. 

7. Real-World Consequences and Chain-Reaction Risk

Recent high-profile failures demonstrate that even when composite tanks contain only inert gas, the consequences of sudden rupture can be catastrophic. In the case of Starship Ship 36, the tank contained only nitrogen, yet the blast and debris damaged surrounding systems sufficiently to destroy the entire vehicle.

Now consider stationary hydrogen storage facilities, where dozens or even hundreds of COPVs, each holding hydrogen at 500+ bar, are arranged side by side. A single tank rupture could hurl high-velocity debris into adjacent vessels, initiating a chain reaction that may engulf the entire installation in a fireball. The S-36 incident underscores that even rigorously manufactured aerospace-grade COPVs are susceptible to sudden failure, emphasizing the structural vulnerability inherent in conventional composite overwrap designs.

Standard certification procedures typically include impact tests on empty tanks, such as dropping a vessel from a height of 3 meters onto a rigid surface. While these tests assess basic mechanical robustness, no standardized impact tests are performed on tanks pressurized to their design pressure. As a result, the behavior of fully loaded tanks under realistic combined stress and impact conditions is not directly evaluated.

In service, a tank is pressurized to hundreds of bars, with the composite wall already under significant hoop and axial tensile stress, particularly near the inner surface. Any external impact superimposes localized bending on top of these pre-existing stresses, amplifying strain where cracks are most likely to initiate and propagate. Testing empty tanks removes this critical interaction entirely, systematically underestimating rupture risk under realistic conditions. Numerous studies and postmortem analyses confirm that catastrophic failures in composite tanks often originate at the inner wall under combined loading—yet current certification protocols do not replicate this scenario.

How Flexyshell Addresses Pressurized Impact

Flexyshell fundamentally changes how a pressure vessel responds to high-pressure impact. Instead of forcing a brittle composite wall to resist both pre-stressed axial and hoop loads and local bending, the flexible cylindrical membrane redistributes stresses elastically. Local impacts are absorbed as membrane tension rather than concentrating strain on the inner wall, preventing crack initiation.

The Flexyshell design also removes the risk of generating high velocity debris at its source. Its flexible membrane and dense tendon lattice act as a self-contained pressure system and integrated safety mesh. If a membrane rupture ever occurs, internal pressure escapes locally through the breach while the tendon network intercepts and traps any debris — preventing the uncontrolled release that makes rigid COPV failure so destructive. Furthermore, should external debris strike the vessel, the tendon lattice carries the load in pure tension, and the flexible shell deforms elastically, ensuring the vessel remains intact and resists catastrophic rupture.

Together, these mechanisms make Flexyshell inherently resilient to the high-pressure impact scenarios that current composite tanks cannot safely withstand.

8. Structural Integration and Modular Safety

Conventional pressure vessels are passive components that require heavy external frames or protective shells, adding cost and mass while providing no structural contribution to the host system.

Flexyshell modules invert this logic: the tank itself becomes a structural element.
The end dome systems function as load-bearing nodes, transferring forces directly into the tendon network. This enables each pressurized module to participate in carrying external bending, shear, and axial loads without exposing the pressure membrane to compression or buckling. The result is a storage system that doubles as a self-supporting structure — inherently stable under both internal and external loads.

This design also introduces a new dimension of safety integration. Because the membrane does not carry axial or bending loads, the pressure chamber can be made dismantlable, with sealed interfaces that experience no mechanical stress. This feature makes possible a tank-in-tank containment system, where each pressurized module can be enclosed within an outer safety shell. The outer shell serves as an energy-absorbing buffer and gas containment layer, forming a multi-stage safety cascade.

The modular, separable construction also allows retrofitting of existing storage systems with outer safety envelopes, converting legacy tanks into effectively fail-safe configurations.

9. Scalable Architecture

 Multiple cylindrical membrane sections can be joined end-to-end to form much longer vessels; the same end dome systems and BOP interfaces are reused, and only the tendon sets are lengthened or multiplied. In practice this means:

  1. A long vessel is assembled by adding standard cylindrical sections together (not by redesigning the wall).
  2. End dome system and BOP remain identical — only tendon length/quantity and the extra cylinder sections change.
  3. Very long vessels can be assembled on-site (ships, platforms, industrial yards) where transport limits or application scale demand it.

Because end dome system and BOP are the relatively complex, higher-cost items and the cylindrical sections + tendons are simple, high-volume components, cost grows much more slowly than vessel length. Standardising end dome system/BOP and mass-producing membrane sections/tendons delivers economies of scale.

Multiple cylindrical sections can be joined end-to-end to build vessels of virtually any required length, using the same end dome systems and BOP interfaces—only tendon length or quantity changes. Because these two components (membrane sections and tendons) are the simplest and lowest-cost parts, a vessel with twice the storage capacity costs far less than twice as much.
Moreover, long Flexyshell vessels can be assembled directly on site, avoiding the impracticality of transporting or lifting 50- to 100-metre-long rigid tanks. Sections are joined, tendons put in place, the vessel is pressurised—and it’s ready for service.

 

In summary, while COPVs represent the pinnacle of rigid-wall pressure vessel evolution, they remain limited by the physics of rigidity itself.
The Flexyshell concept departs from this path entirely — transforming internal pressure from a threat into a stabilizing force, and replacing brittle resistance with cooperative tension.

By resolving all primary loads into tensile form, Flexyshell eliminates the fundamental stress conflicts of rigid composites, offering a storage architecture that is lighter, safer, scalable, and inherently more forgiving — a foundation for the next generation of hydrogen infrastructure.

This invention represents not just an incremental improvement but a fundamental change in the way high-pressure gases are contained, transported, and utilized.