A Propellant Is the Gas That Pushes the Product Out of an Aerosol

A propellant is the pressurised gas that pushes the product out of an aerosol can and decides whether it comes out as a fine mist, a jet, a foam or a gel. There are four families: hydrocarbons (propane, butane and isobutane), dimethyl ether (DME), compressed gases (nitrogen, CO₂ or air) and fluorinated gases. The choice depends on the formula, the use and the regulations.

According to the European Aerosol Federation (FEA), the propellant makes up between 5% and 90% of the contents of the can. It can be a liquefied gas, which also acts as a co-solvent for the formula, or a compressed gas, which only fills the free space above the liquid.

Which Propellant Family Fits Your Formula?

It is called a propellant gas, and there is no single one. In most aerosols today it is a blend of liquefied hydrocarbons; water-based products usually use DME, and products that must not be flammable use a compressed gas or a fluorinated gas. The four families behave like this:

The state in the can sets the behaviour. A liquefied gas is partly liquid and partly vapour, and as long as some liquid remains the pressure stays almost constant until the can is empty. A compressed gas loses pressure as the product is used, and its spray is usually coarser than that of a liquefied gas.

To choose a family, start with two questions about your product. If the formula contains water, look first at DME or a compressed gas; if the product must not be flammable, rule out hydrocarbons and DME and choose between a compressed gas and a fluorinated gas.

Hydrocarbons or DME: Which to Choose

A hydrocarbon propellant is liquefied petroleum gas (LPG): propane, butane and isobutane, alone or blended. They are the most widely used propellants in the aerosol industry: colourless, odourless once purified, flammable and highly soluble in oil-based or alcohol-based formulas.

Each one gives a different pressure. Propane gives the highest, butane the lowest and isobutane sits in between, so the vapour pressure is adjusted by blending them in different proportions. That is why almost no aerosol uses a single pure hydrocarbon.

Dimethyl ether (DME) is the other major liquefied propellant. It is partly soluble in water, which makes water-based aerosols possible, and it has a lower heat of combustion than hydrocarbons, although it is still a flammable gas. The practical rule: oil-based or alcohol-based formula, LPG; water-based formula, DME.

💡 Formulator's rule: if the sample sprays too hard or falls short, ask for the blend ratio to be adjusted before changing gas family. Mixing propane and isobutane in different proportions is the usual way to reach an intermediate pressure without losing solubility.

The Properties That Decide the Choice

Choosing a propellant rests on five technical parameters that are assessed together, never one at a time:

Three product criteria come on top. The type of formula, water-based or oil-based, rules some propellants out from the start; the output, mist, foam or gel, calls for different pressures; and the target market decides which gases are legal and how flammability is labelled.

Cost matters too: the latest fluorinated gases are much more expensive than hydrocarbons. In practice, most formulas are solved with hydrocarbon blends, or with DME for water-based ones, and fluorinated gases are kept for products that must be non-flammable.

Why Are CFCs No Longer Used?

Chlorofluorocarbons (CFCs) destroy the ozone layer. The Montreal Protocol of 1987 ordered their phase-out, and the European aerosol industry voluntarily stopped using them in 1989, according to the FEA. Their replacements, HFCs, do not harm the ozone layer but are powerful greenhouse gases, and the Kigali Amendment to the same protocol requires them to be cut worldwide.

In the European Union the rules are set by Regulation (EU) 2024/573 on fluorinated gases, which bans placing these aerosols on the market:

Technical aerosols are exempt when the fluorinated gas is needed to meet national safety standards or for medical applications. The 2030 ban also covers HFO-1234ze, which the regulation lists among fluorinated greenhouse gases even though its global warming potential is 1.37.

Today, the aerosol industry has primarily shifted to flammable liquefied propellant gases (hydrocarbons and dimethyl ether) for 'general' aerosols but still uses fluorinated propellant gases in some 'technical' aerosol dispensers to formulate non-flammable products for safety reasons.

What to Decide Before Filling

The propellant is the last thing to go into the aerosol. First the concentrate is dosed into the empty can, then the valve is crimped on and, with the can already closed, comes propellant injection, under pressure and through the valve itself. A weight check confirms the dose and every unit goes through a hot water bath at 50 °C that reveals any leak before it reaches the market.

That order explains why propellant, valve and formula are decided together: the valve has to accept filling with the chosen gas and the formula has to live with it inside the can for its whole shelf life.

So decide the propellant at the same time as the valve, not afterwards: if you change gas once the valve is chosen, ask for confirmation that the valve accepts filling with the new gas.

Your next task is to write down three answers: whether your formula is water-based or oil-based, how it must come out and whether it may be flammable. With them, Ilerspray's laboratory, which fills with LPG, DME and CO₂, can propose the gas or blend for your made-to-order aerosol from the first sample.