If you searched for “hydrogen drone tank weight comparison,” what you got was a row of vendor product pages with no head-to-head numbers. This article ranks every commercially-available 350-bar Type IV cylinder for hydrogen drones by the only metric that matters at the airframe level: gH₂ stored per kg of empty cylinder mass. Numbers are sourced from public datasheets and cited per row. Where data is missing, that’s flagged.

Why this metric and not “lightest cylinder”

“Lightest cylinder” is the wrong question. A 0.5 kg empty cylinder that stores 8 g H₂ is worse than a 1.3 kg cylinder that stores 75 g H₂, because the airframe carries every kg whether or not it’s full. The right metric for any UAV mass-budget calculation is:

gravimetric ratio = (gH₂ stored at NWP) / (cylinder empty mass)

For a Type IV cylinder at 350 bar at 20 °C, hydrogen density is ~24 g/L. gH₂ stored = volume × 24. For a 3 L cylinder that’s 72 g; for a 6.8 L that’s ~163 g; for a 0.5 L it’s 12 g. Ratio = gH₂ / cylinder mass.

The comparison table

^† Hexagon Purus does not publish drone-class cylinder masses on its standard datasheets; values are estimated from the published Type IV mass-scaling curves and aerospace-class line cylinders.
^est. = competitor mass not directly published; estimated from aggregate datasheets and competitor product pages.
Where vendor data is unavailable, MEYER’s mass-scaling reference (K_PET = 0.000280 kg/L·bar of burst) is used as the comparison baseline. Real values may differ ±10–15% per vendor.

What the numbers say

• Type IV PET (Meyer HDRX) leads at the small end and the medium end — ~48–51 gH₂/kg in the 3–9 L band, where most hydrogen drones operate.
• Type IV HDPE-lined competitors (Hexagon, Hfsinopower) are roughly 10–20% heavier per litre at the same pressure because the HDPE liner is thicker (~4 mm vs PET’s ~0.3 mm).
• Type III aluminium-lined drops to ~25 gH₂/kg — about half the gravimetric efficiency of Type IV PET. This is the headline difference that shows up in fleet TCO calculations.
• All-metal Type I drops to ~11 gH₂/kg — below the threshold of practical drone use; included for reference.
• Cellen cartridge (700 bar) trades higher pressure for smaller envelope; the gravimetric ratio is similar to MEYER but the cartridge is single-use rather than refillable in field.

What this means for drone selection

For a 15 kg-class hydrogen drone, the difference between a Type IV PET and Type III cylinder of the same H₂ mass is roughly 1.2 kg. On a typical airframe, that translates to ~3 minutes of additional flight time per sortie or equivalent payload uplift.

For fleet operators, the cumulative effect over 5 years is the metric that matters. We’ve built a 5-year cost-of-ownership calculator that combines the mass delta with replacement cycles, revenue per sortie, and cycle-life limits.

Caveats and what’s not in the table

• Valves and PRDs are not included in the cylinder mass — typical valve adds 100–250 g depending on cycle-life rating.
• Permeation rate is not in the table — Type IV PET permeates faster than Type III at long stand times. For daily-fill drones this is irrelevant; for long-storage applications, consult our permeation calculator.
• Cycle life is not in the table — a major Type III/IV trade-off. See the TCO article.
• Vendors not in the table: NPROXX, Quantum Fuel Systems, Faber, and several Chinese vendors don’t publish drone-class data. Hexagon does not publish drone-class data (their drone-relevant cylinders are sold via OEMs like H3 Dynamics).

Live the data — your way

If you’re selecting a tank for a specific airframe, plug the numbers into our tools:

• COPV mass calculator — estimate cylinder mass for your specific volume and pressure
• H₂ pressure tier calculator — choose between 350, 500, and 700 bar storage
• 5-year cost of ownership calculator — compare Type III vs Type IV PET for your fleet operation

Read more

• How to specify a hydrogen tank for a fuel-cell UAV
• Type III vs Type IV PET for UAV fleets — 5-year TCO
• Browse the full COPV catalog

Most aerospace and industrial cylinders ship with a service-life stamp — typically 15 or 20 years — after which they’re pulled from service whether they’ve been used or not. NLL (No Limited Lifespan) qualification removes that date entirely. The cylinder stays in service indefinitely, subject to periodic inspection. The difference between the two is structural, historical, and worth real money over a fleet’s lifetime.

Why cylinders expire in the first place

The expiration-date concept is a 1980s artefact of all-metal cylinders. Steel and aluminium cylinders fatigue under repeated pressure cycling — every fill propagates micro-cracks at stress concentrations (bosses, neck threads, weld zones). After enough cycles, one of those cracks reaches critical length and the cylinder bursts. The 15-year stamp is a calendar-based proxy for “we don’t have a way to non-destructively inspect for fatigue at this level, so retire the cylinder before it gets dangerous.”

The proxy was conservative but defensible: a 15-year window covered the worst-case usage profile (daily-fill, high-cycle service like SCBA or industrial gas) for the metal cylinders of the time. For occasional-use cylinders the date was wasteful — perfectly serviceable hardware retired because the calendar said so — but the regulatory simplicity won out.

What changed with Type IV polymer-lined construction

A Type IV COPV puts the entire pressure load on the carbon-fibre overwrap. The polymer liner is a gas-tight bladder, not a structural element. Two things follow:

• The liner doesn’t fatigue the way metal does. Polymer fatigue is dominated by chain-scission and crystallinity changes, both of which are slow at room temperature and inspection-detectable.
• The carbon-fibre overwrap doesn’t fatigue meaningfully either at the working stresses Type IV cylinders see. CFRP fatigue is well-characterised: at <30% of UTS, a properly cured laminate sees essentially infinite cycles to failure. Type IV cylinders are typically operating at 25–30% of UTS by design.

The combination removes the two failure modes that drive metal-cylinder service life. What remains — UV degradation, impact damage, internal corrosion (if any), elastomer ageing in the seals — is detectable by periodic visual and hydrostatic inspection. NLL qualification simply codifies this: the cylinder stays in service as long as it passes the inspection programme.

What NLL actually requires

NLL is not a free pass. To qualify a Type IV cylinder for NLL service under ISO 11119-3 / EN 12245, the design must demonstrate:

• Cycle life testing beyond expected service: typically 10,000+ cycles at working pressure, no leakage or burst.
• Sustained-load testing: hold at working pressure for extended duration, no liner failure.
• Periodic inspection programme: typically 5- or 10-year hydrostatic plus annual visual. Failed inspection retires the cylinder; passed inspection extends service indefinitely.
• Traceability: every cylinder carries a record of its inspection history.

The MEYER HDRX family is qualified to NLL. Each cylinder ships with the documentation needed to enrol it into a periodic inspection programme.

What this means in money

For a fleet of 100 cylinders over a 30-year procurement horizon:

• 15-year service-life cylinders: replaced once at year 15. Total cylinder count purchased: 200. Plus 100 disposal events.
• 20-year service-life cylinders: replaced at year 20. Total purchased: 200 (same count, different timing).
• NLL cylinders: no replacement, just inspection. Total purchased: 100.

Even at parity unit cost, NLL halves the lifetime cylinder spend. For aerospace cylinders that often run €3–8k each, that’s €300–800k saved per 100-cylinder fleet — without counting downtime, replacement logistics, and qualification re-flights for the new units.

When 15-year service life is still the right answer

NLL is not always available. The cases where service-life cylinders remain the right choice:

• All-metal Type I cylinders — the failure mode (metal fatigue) is fundamentally different and NLL is not achievable.
• Older Type III aluminium-lined designs not qualified to NLL. Some are; many aren’t.
• Programmes that require a calendar retirement for regulatory reasons (some hydrogen-vehicle regulations, some breathing-apparatus standards).

For aerospace, UAV, and CubeSat applications, NLL Type IV is now the cost-effective and cycle-life-optimal choice unless a specific regulation forces otherwise.

What to ask suppliers

• Is this cylinder qualified to NLL or to a service-life date? Get the answer in writing.
• What’s the inspection programme: hydrostatic interval, visual interval, who can perform it?
• What documentation ships with the cylinder for NLL enrolment?
• What happens if a cylinder fails inspection — repair, retest, or scrap?

The right answer to the first question is “NLL, with a 5-year hydrostatic interval per ISO 11119-3.” If the supplier defaults to a 15-year stamp without offering NLL, you’re looking at older qualification.

Read more

• Type 3 vs Type 4 COPVs: which is right for your aerospace application?
• Aerospace COPV compliance: TPED, PED, ISO, EN explained
• COPV Selector — match your spec to the right format

“Type III aluminium-lined cylinders are the conservative choice for hydrogen UAVs” is industry orthodoxy. The spreadsheet, run honestly, says otherwise — at least for daily-fill commercial fleets. Here’s the 5-year cost-of-ownership math, with the numbers an integrator would see in real procurement.

The fleet we’re modelling

Sample fleet:

• 100 hydrogen-fuel-cell UAVs in a commercial inspection / surveying / cargo operation
• Each UAV flies 4 sorties per working day, 250 working days per year = 1,000 sorties/year/UAV
• One cylinder per UAV (some operations swap cylinders mid-day; the math scales similarly)
• Cylinder spec: 3-litre, 300 bar working pressure, M18 × 1.5 thread

Each cylinder sees ~1,000 fill cycles per year. Over 5 years that’s 5,000 cycles per cylinder. Hold this number — it determines everything.

Type III aluminium-lined: the legacy default

• Mass: ~2.5 kg for a 3-litre at 300 bar
• Service life: in legacy industrial use, Type III aluminium-lined cylinders are spec’d at 5,000–15,000 cycles. To compete with MEYER® on weight, several Type III makers now publish UAV-class designs qualified to as little as 500 cycles. At 1,000 fill cycles per year, that is a retirement event inside year 1 — plus the 15- or 20-year calendar cap. Lighter Type III is not cheaper Type III: it front-loads the replacement bill and pushes the design closer to its fatigue envelope, raising failure-mode risk.
• Replacement timing: at 1,000 cycles/year, expect cylinder retirement at year 5–10. Conservative planners assume 5 years.
• Indicative unit cost: €1,200 (varies by supplier and qualification scope)

Over 5 years for 100 cylinders: €120,000 in cylinder spend, with a near-certain replacement event at year 5 — adding another €120,000 if you continue the operation into year 6.

MEYER®: the lighter alternative

• Mass: ~1.3 kg for the HDRX-030 (3-litre, 300 bar). About 1.2 kg lighter than Type III.
• Service life: 10,000+ cycles, NLL qualified — no calendar replacement.
• Replacement timing: none expected within 5-year horizon.
• Indicative unit cost: €1,800–2,200 for low-volume orders, falling to €1,400–1,700 at fleet scale (100+ cylinders).

Over 5 years for 100 cylinders at €1,800 unit cost: €180,000 in cylinder spend. Higher upfront — that’s the part Type III defenders point to. But the spend stops there.

The real comparison: per-flight revenue

The 1.2 kg mass delta translates to flight time and payload. For a 15-kg-class hydrogen UAV, 1.2 kg saved on the cylinder typically buys ~3 minutes of additional flight time per sortie (or equivalent payload uplift).

• Commercial inspection sortie: typical revenue €150–300, dependent on flight time
• 3 minutes additional flight per sortie — roughly +5–10% utilisation on a 30-minute mission
• For 100 UAVs × 1,000 sorties/year × €15 incremental revenue per sortie = €1.5M/year in fleet-level revenue uplift

The €60k extra upfront cylinder cost (MEYER® vs Type III) is recovered in ~2 weeks of fleet operation. Over 5 years, the revenue delta is >€7M. That’s before counting downtime savings from no replacement event.

5-year TCO summary

When Type III still wins

Three cases where Type III aluminium remains the right answer:

• Long-duration storage of hydrogen or helium — the polymer liner permeation rate (~30%/month for H₂ at 300 bar) becomes meaningful when the cylinder sits filled for weeks. Daily-fill UAV operations don’t see this.
• Programmes that already qualified Type III — re-qualification cost can dwarf the operational savings.
• Cost-floor operations where unit price is the dominant constraint and mass / cycle life don’t translate to revenue.

For commercial daily-fill UAV fleets — which is most of the H₂-drone industry today — none of these conditions hold.

Run your own numbers

The cost model above uses indicative figures. Your actual fleet will have different sortie revenue, sortie length, fleet size, and cylinder unit cost. Run the math with your own numbers in our 5-Year Cost of Ownership Calculator — the comparison is built on the same model, with editable inputs.

Read more

• 5-Year Cost of Ownership Calculator
• NLL vs 15-year service life
• Type 3 vs Type 4 COPVs comparison
• Specifying a hydrogen tank for a fuel-cell UAV

The default-to-highest-pressure assumption is wrong about half the time. 700 bar is real engineering work — the cylinder gets thicker, the regulator gets heavier, the seals get harder, the refuelling infrastructure gets sparser. This framework shows when 700 bar is worth it and when 350 or 500 bar wins on system mass.

The hydrogen-density curve, honestly

The first instinct on any hydrogen project is “more pressure = more H₂ per litre.” That’s correct, but the relationship is sublinear because hydrogen is non-ideal at high pressure — the compressibility factor Z rises above 1.0 above 200 bar, meaning each additional bar buys progressively less density.

• 200 bar: ~14 g H₂ per litre
• 300 bar: ~21 g/L
• 500 bar: ~32 g/L
• 700 bar: ~41 g/L
• 1000 bar: ~48 g/L

700 bar gives ~95% more H₂ per litre than 300 bar — but only ~28% more than 500 bar. The marginal density gain falls off above 700.

The cylinder-mass curve, also honestly

Type IV cylinder mass scales approximately linearly with burst-pressure × volume (the burst PV product). For the same volume, going from 300 to 700 bar at the same safety factor more than doubles the cylinder mass:

• 3 L at 300 bar (HDRX-030): 1.30 kg
• 3 L at 500 bar: ~2.0 kg
• 3 L at 700 bar: ~2.8 kg

To store the same H₂ mass, you can use a smaller cylinder at higher pressure. The right comparison is hydrogen-mass-per-cylinder-mass, the gravimetric efficiency:

• 3 L at 300 bar: 63 g H₂ / 1.30 kg cylinder = 4.6% gravimetric
• 2 L at 500 bar: 64 g H₂ / 1.4 kg cylinder = 4.4% gravimetric
• 1.5 L at 700 bar: 62 g H₂ / 1.4 kg cylinder = 4.2% gravimetric

The gravimetric efficiency is roughly flat across the pressure range — physics doesn’t give you a free lunch on H₂ storage. The real differentiation is volumetric envelope: 700 bar lets you hit the same H₂ mass in a smaller cylinder. If volume is more constrained than mass, 700 bar wins. If mass is the constraint, it doesn’t.

System-level mass: regulator, valves, fittings

The cylinder isn’t the only mass that scales with pressure. A complete H₂ fuel system includes:

• Regulator: a 700-bar inlet regulator is typically 40–60% heavier than a 300-bar inlet regulator (thicker walls, larger seal seats, often two-stage for stability)
• Service valve: same scaling
• Fittings, lines, brackets: minor but additive
• Fill nozzle: 700 bar TK17 / TK25 fittings are larger and heavier than 300 bar equivalents

For a small UAV, the system-level mass penalty of going from 300 to 700 bar is typically 0.3–0.6 kg over and above the cylinder mass change. On a 15-kg-class drone that’s 2–4% of gross weight.

Refuelling infrastructure

700 bar refuelling stations exist but are sparse. Geographic considerations:

• EU: most public H₂ stations dispense at 700 bar (light vehicles) and 350 bar (heavy vehicles). Industrial fill is commonly 350 bar.
• US: 700 bar dominant in California, 350 bar elsewhere. Industrial-grade 350 bar widely available.
• Japan: standardised on 700 bar.
• Custom / on-site filling (industrial, military, R&D): typically 200–350 bar. 700 bar requires specialised compressor and storage.

For UAV operators that depend on commercial refuelling stations, 700 bar opens access to passenger-vehicle infrastructure but limits the rest of the world to 350. For programmes with on-site fill (most aerospace and defence), 350 bar is usually the practical ceiling without significant capital investment in compressors.

Decision framework

Pick 700 bar when:

• Volume envelope is more constrained than mass (CubeSat, certain UAV airframes)
• You can refuel from a 700-bar source (EU, Japan, on-site investment justified)
• The system mass penalty is acceptable in your weight budget

Pick 500 bar when:

• You want most of the density benefit without the full system mass penalty
• Your cylinder volume budget is moderate, not severely constrained

Pick 300–350 bar when:

• Mass is your dominant constraint
• You’re operating off industrial fill infrastructure
• Cylinder volume is not envelope-limited
• You want to maximise gravimetric efficiency on a per-cylinder basis

Run the numbers for your project

The trade-off is enough variables that no single rule fits. Use our Hydrogen Pressure Tier Calculator to compare 300, 500, and 700 bar for your specific volume, mass, and envelope constraints.

Read more

• Hydrogen pressure-tier decision calculator
• COPV mass & performance calculator
• Specifying a hydrogen tank for a fuel-cell UAV
• COPV Selector — match your spec to the right format

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:

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.