Cosmetic Aerosol Packaging: Pressure & Vacuum Requirements (Buyer's Guide)

What "pressure requirement" means for a cosmetic aerosol

An aerosol is, by definition, a non-refillable container holding a product and a propellant under pressure, with a release device that turns the contents into a spray, foam, or powder. The propellant is what creates the pressure. The law does not care how clever your formulation is; it caps the pressure the can may reach at 50°C, because that is the temperature a container can see in a parked delivery truck or a summer warehouse.

In the EU, the Aerosol Dispensers Directive 75/324/EEC sets the ceilings by gas type. The current text limits the pressure at 50°C as follows:

The same directive also sets a minimum test pressure for the empty container: at least 10 bar for cans filled below 6.7 bar at 50°C, and 50% above the internal pressure at 50°C for everything filled higher. The full text is published on the UK legislation site, which reproduces the directive annex verbatim: Directive 75/324/EEC, Annex 3.1.

The reversed-epsilon mark, and what it actually proves

A compliant EU aerosol does not carry a CE mark. It carries the reversed epsilon (ϵ) symbol. That mark is the manufacturer's statement that the can passed the pressure and filling tests and meets the directive. If you are sourcing finished aerosols or having them filled, the reversed epsilon on the base or shoulder is the first thing to check: no symbol, no lawful EU placement, regardless of how good the spray feels. Labeling of the pack itself falls under ISO 22715:2006, the international standard specifying requirements for the packaging and labeling of cosmetic products offered for sale or free distribution (ISO 22715:2006).

Vacuum dispensing is a different physics problem

An airless pump bottle is not an aerosol and is not pressurized with a propellant. A piston or pouch sits at the bottom of the bottle; as you press the actuator, a spring or the returning atmosphere draws product up through the orifice. The headspace stays near atmospheric pressure, and there is no compressed gas pushing the formula. That is the whole point: sensitive actives such as vitamins, peptides, or unsaturated oils are never in contact with a propellant and see far less oxygen once the seal is closed.

For a buyer, the trade is clear. Aerosols win for sprays, mists, and foams where you need a gas to do the work. Airless pumps win for serums, lotions, and oxidation-sensitive creams where you want to keep air out. The table below sets the two side by side.

If your line is airless, the specification work shifts from pressure to evacuation rate and piston seal life. Our write-up on airless pump system specifications and the companion piece on piston evacuation rate cover those numbers in detail.

Container material sets your pressure headroom

The directive treats metal, glass, and plastic differently because they fail differently. Metal monobloc and three-piece cans take the highest ceilings and are the default for true aerosols. Glass is allowed only with limits: plastic-coated or permanently protected glass containers are capped at 220 ml total capacity and must resist at least 12 bar (compressed or dissolved gas) or 10 bar (liquefied gas); unprotected glass is limited to 150 ml and a 12 bar test. Plastic (laminate or molded) aerosol containers exist but need the same pressure qualification and are less common in cosmetic sprays. When a formula is aggressive to metal, the answers are usually a lined can or a move to airless glass, not a thinner wall.

For any pressurized pack aimed at consumers, the closure also matters. A pressurized container needs a closure that will not loosen in transit, and for certain product types a child-resistant closure is part of the compliance picture. See our guide to child-resistant closures for cosmetics for the design and compliance trade-offs.

Propellant choice is where pressure is won or lost

Most pressure trouble starts at the filling table, not the can plant. Liquefied gases (the dimethyl ether and propane or butane blends used in cosmetic sprays) sit as a liquid in the can and generate vapor pressure that rises steeply with temperature. Compressed gases (nitrogen, compressed air) give a gentler, flatter pressure curve but a weaker spray. The right propellant load is a balance: enough to atomize the formula, not so much that you breach the 50°C ceiling.

Published filling studies put the optimum in a narrow band. One investigation of aerosol evacuation found the best results at a propellant mass fraction of 13.79%, where the excess pressure was 0.4 MPa and stayed inside the acceptable 0.2 to 0.6 MPa window (aerosol propellant optimization study, Zenodo). That is a research figure, not a spec for your product, but it shows why propellant percentage is treated as a controlled variable on a real filling line rather than a guess.

Transport and storage: pressure follows temperature

The 50°C limit is not arbitrary. It is the temperature used for the hot-water-bath final test, where every filled can is heated until its internal pressure equals what it would reach at a uniform 50°C, then checked for leaks, permanent distortion, or burst. A can that passes that test is safe through normal warehousing and road transport. For air freight and cross-border shipping, aerosols are also treated as pressurized dangerous goods under the UN and ICAO rules, which is why net fill weight and proper hazard labeling are part of the same specification, not an afterthought.

A five-point specification checklist for buyers

Before I release an aerosol or airless line for tooling, these five items are on the sheet:

• Pressure class: confirm the propellant type and that the 50°C pressure lands under the 12, 13.2, or 15 bar ceiling for that gas.
• Conformity mark: reversed epsilon on the can for any EU aerosol; verify the filler's test records.
• Container qualification: material, total capacity, and minimum test pressure matched to the directive's glass and metal limits.
• Formula compatibility: propellant-to-product contact, preservative need, and oxygen sensitivity (airless if sensitive).
• Closure and transport: closure torque or CR requirement, plus UN or ICAO net-fill and hazard labeling for shipping.

Spray character is its own spec. Our notes on fine-mist sprayer atomization and the perfume spray bottle sourcing guide turn "make it a nice mist" into measurable numbers you can send to any supplier.

Frequently asked questions

What is the maximum internal pressure allowed in a cosmetic aerosol?

Under Directive 75/324/EEC the internal pressure at 50°C must not exceed 12 bar for liquefied flammable gases, 13.2 bar for liquefied non-flammable gases, or 15 bar for compressed or dissolved non-flammable gases. The empty container also has a minimum test pressure of at least 10 bar.

Does an airless pump use pressure like an aerosol?

No. An airless pump is not pressurized with a propellant. A piston or pouch and a spring draw product up at near-atmospheric pressure, which is why airless packs are chosen for oxygen-sensitive formulas rather than for sprays.

What does the reversed-epsilon symbol mean on an aerosol can?

It is the conformity mark required by Directive 75/324/EEC. It tells the market that the dispenser passed the pressure and filling tests. An EU aerosol without it cannot be lawfully placed on the market.

How does propellant choice affect aerosol pressure?

Liquefied gases give strong atomization but a pressure curve that climbs fast with temperature, so the fill percentage must be controlled tightly. Compressed gases give a flatter curve and weaker spray. The propellant load is set to stay under the 50°C ceiling while still delivering the spray quality the formula needs.

Conclusion

Pressure and vacuum are not styling details; they are the load-bearing facts of an aerosol or airless pack. The 12 to 15 bar ceiling, the reversed-epsilon mark, the container test pressure, and the propellant load are the four numbers that decide whether a format is safe, legal, and pleasant to use. Get them on the specification sheet before tooling, and most field failures simply never happen. If you want those numbers worked out for your specific formula and market, get a tailored aerosol packaging spec sheet from our engineering team.