Bag-on-Valve Keeps the Product Apart from the Gas That Drives It
Bag-on-valve (BOV) is an aerosol system in which the product sits inside a bag welded to the valve and the gas stays outside it, in the can. The bag is laminated, and the gas, compressed air or nitrogen, fills the space between it and the can. When you press, the gas squeezes the bag and the product comes out pure, never mixing with the propellant. It suits sensitive formulas, water-based ones and products that must be non-flammable.
How Bag-on-Valve Works and What to Check in Your Formula
In a conventional aerosol the propellant and the formula share the can: the liquefied gas mixes with the product and comes out with it. A BOV has two compartments. Inside the bag there is only the product; outside it, the pressurising gas, which is not part of the formula and does not come out when you press.
- Bag
- multilayer laminate, aluminium and polymers
- Valve
- welded to the bag
- Can
- metal, usually aluminium
- Gas
- compressed air or nitrogen
Filling runs in the reverse order of a classic aerosol. First the valve, with the bag already welded to it, is placed in the can; then the gas is injected between the bag and the can and the valve is crimped; only then is the product filled through the stem, straight into the bag. Finally the actuator is fitted.
Because the gas is compressed rather than liquefied, the pressure drops as the bag empties. For a metal aerosol with a non-flammable compressed gas, the EU Aerosol Dispensers Directive 75/324/EEC sets a maximum of 15 bar at 50 °C, against 12 bar for a flammable liquefied gas.
That pressure drop is the first thing to check for your product: if it needs the same output from the first press to the last, test the BOV sample nearly empty as well, not only freshly filled.
Which BOV Benefit Does Your Product Need?
Full separation of product and propellant is the basis for every other benefit:
- It works in any position, even upside down, because the gas presses on the bag equally from every angle.
- The bag empties almost completely and leaves very little product unused.
- The formula never touches air or gas, which protects its stability and can reduce the need for preservatives.
- The spray is even and does not chill the skin, because no liquefied gas comes out and evaporates.
- With air or nitrogen, the propellant is neither flammable nor a source of volatile organic compounds.
Go through the list with your product and mark the benefits your customer will actually notice. If you mark none, a conventional aerosol does the same job with a cheaper valve.
💡 Technical tip: before asking for samples, write down three facts about your formula today: whether it is very viscous, whether it must work upside down and whether it may be flammable. Very viscous products have a practical limit on what can pass through the stem, so that fact decides first whether BOV is viable.
Does Your Product Fit BOV?
BOV fits wherever the priority is formula purity and stability against air:
| Sector | Typical products |
|---|---|
| Cosmetics | Face mists, sun protection, shaving gels |
| Pharmacy | Saline solutions, burn gels |
| Food | Spray oils and dressings |
| Household | Air fresheners and cleaners |
| Industry | Lubricants and maintenance products |
The common thread is a formula that must not come into contact with the propellant, or a product that has to work in any position.
Apply it to your product: if your formula spoils in contact with gas or air, BOV is the candidate. If you only need it to work in any position, a 360 valve on a conventional aerosol achieves that too.
When Bag-on-Valve Is Not the Right Choice
BOV does not suit everything. Products that need the gas to leave with the formula lose their function without it: a dry shampoo uses the push of the gas to spread the powder, and a voluminous foam forms when the liquefied propellant expands on the way out.
Nor does it suit very high viscosity formulas, which hit the flow limit of the stem. And a BOV valve costs considerably more than a conventional valve, so the system is mainly kept for products where separation adds value the end customer will pay for.
What You Can Say About Bag-on-Valve Sustainability
On several counts, yes. Using air or nitrogen removes hydrocarbons from the propellant, and with them their flammability and volatile organic compounds; and since the bag empties almost fully, less product is wasted.
The can follows the same path as any metal aerosol. The FEA points out that aerosol cans are generally made of steel or aluminium, recyclable materials with market demand, and argues for including empty aerosols in packaging collection schemes. The multilayer bag, by contrast, is a composite material that stays inside the can and cannot be separated by the consumer.
If you plan to use sustainability as a selling point, base it on what the system really changes (a non-flammable propellant, no volatile organic compounds, less product wasted) and do not promise that the whole pack is recycled: the bag stays inside.
Recycling is FEA's preferred route to recover the value of used (i.e. empty) aerosols.
Ilerspray does not fill bag-on-valve yet: we are studying which gases we will be able to work with in this technology. If your product calls for it, say so when you send us your aerosol contract manufacturing project: it helps steer that study and decide which system suits it in the meantime.
