Type 3 vs Type 4 COPVs: Which is Right for Your Aerospace Application?
If you are specifying a composite pressure vessel for an aerospace, UAV, or satellite system, the first decision is almost always: Type 3 or Type 4? The choice affects mass, cycle life, cost, and qualification path. This guide explains the differences in plain engineering terms.
Quick definitions
Composite Overwrapped Pressure Vessels (COPVs) are classified by liner material:
- Type 1: All-metal (steel or aluminium). No composite.
- Type 2: Metal liner with hoop-wrapped composite around the cylindrical section only.
- Type 3: Metal liner (typically aluminium) with full composite overwrap (cylindrical and dome sections).
- Type 4: Polymer liner (typically PET, HDPE, or similar) with full composite overwrap.
Type 3 and Type 4 are the two technologies that dominate weight-critical aerospace, UAV, and satellite applications. Both use carbon-fibre (CFRP) overwrap to carry the structural load. The only meaningful difference is the liner.
The liner is the whole story
The liner has two jobs: provide a gas-tight barrier (so the cylinder holds pressure) and serve as a mandrel for the composite winding. The composite carries the structural load.
In a Type 3, the metal liner is structurally significant: it shares load with the composite. In a Type 4, the polymer liner is essentially a balloon—it provides the gas seal, and the composite does all the structural work.
This single difference cascades into every other property:
| Property | Type 3 (metal liner) | Type 4 (polymer liner) |
|---|---|---|
| Liner material | Aluminium (typical) | PET, HDPE, or similar polymer |
| Liner role | Load-bearing + barrier | Barrier only |
| Mass | Heavier | Up to ~45% lighter than Type 3 (equivalent capacity) |
| Cycle life | Limited by metal fatigue | Excellent — polymer has no fatigue limit; CFRP-driven |
| Permeation | Negligible (metal seals well) | Slightly higher (polymer is slightly permeable, especially to helium and hydrogen) |
| Cost | Higher per unit (metal liner machining) | Lower per unit at volume; polymer liner is mouldable |
| Service temperature | Wider range | Limited by polymer (typically -40 °C to +85 °C) |
| Field repair | Generally not repairable | Generally not repairable |
| Typical aerospace use | Helium pressurant, propellant tanks where permeation is critical | UAV hydrogen storage, CubeSat propellant, multi-cycle applications |
When to choose Type 3
- Helium pressurant systems where polymer liner permeation is unacceptable
- Wide temperature operation beyond polymer service range
- Single-use or low-cycle-count missions where metal fatigue is not a constraint
- Programs with metal-COPV qualification heritage where requalification cost outweighs the mass savings of a Type 4 switch
When to choose Type 4
- Hydrogen fuel-cell UAVs — mass is the dominant constraint; Type 4 wins on every gram
- Reusable / multi-cycle missions where 10,000+ cycles are required
- Cost-sensitive programs where polymer liner volume manufacturing is a benefit
- Nitrogen, oxygen, or air storage where permeation is a non-issue
- Standard temperature ranges (most UAV, satellite, and ground systems)
The mass argument, in numbers
For a typical 3L cylinder at 300 bar:
- All-metal (Type 1): ~5–6 kg
- Type 3 (aluminium liner + CFRP): ~2.5–3 kg
- Type 4 (polymer liner + CFRP): ~1.3 kg (e.g. MEYER HDRX-030)
For a UAV with a 30-minute mission, that ~1.5 kg saving versus Type 3 directly translates to longer flight time, more payload, or smaller batteries. For a microlauncher upper stage, it translates directly to payload to orbit.
What MEYER builds
MEYER specialises in Type 4 COPVs with PET liners and aerospace-grade CFRP overwrap, in capacities from 0.5 L to 350 L and working pressures up to 700 bar. We do not currently produce Type 3 vessels.
If your application demands the lowest possible mass with multi-cycle operation — UAVs, CubeSat propulsion, microlauncher upper stages, fuel-cell systems — Type 4 is almost certainly the right answer. If your application requires Type 3 specifically (helium pressurant with strict permeation requirements, for example), we are happy to advise on whether a Type 4 with a tuned liner specification can meet your need, or refer you elsewhere.
