As you know from Part 1 of this series, aerosols are a very popular way of dispensing beauty products such as hairsprays, deodorants, and shaving creams.

In Part 2 we explained how aerosol packaging consists of metal cans and some valve hardware that looks simple but is really only slightly less complicated than the Space Shuttle. And in Part 3 we explained how a complicated mixture of chemical goodies (like hairspray polymers, for example) and a potentially explosive gas work together to create your hair style.

But there are still some unanswered questions: How do the liquid and the gas get inside the can? How is the can sealed so the gas doesn’t just evaporate? And once it’s all put together, how do we keep the whole thing from exploding? In this fourth and final installment of Adorable Aerosols, we’ll answer those questions as we explain how aerosols are made.

Aerosols require a special, highly automated manufacturing process. In fact, entire factories are built that specialize in making these products. These factories use long conveyor lines to move the products from station to station where different operations are performed.

Step 1: Preparing the Cans

At the start, the inside of the cans are cleaned with a blast of compressed air to get rid of any dust or dirt that might cause the valve to clog. A clogged valve = an aerosol that won’t spray = a return trip to Walmart for you. So it’s important that the cans are clean before they travel to the next station where they’re filled with liquid concentrate (the goodies in the formula that make it work).

Step 2: Filling

The liquid concentrate is blended in large stainless steel tanks and pumped to a filling station on the conveyor line. At this station, a filling nozzle injects a metered amount of the concentrate into the can. The exact proportions are critical: too much or too little liquid in the can will screw up the spray properties of the finished product. After the concentrate is squirted into the cans, they travel to another station that loosely inserts the valve assembly into the hole on top of the can.

Step 3: Gassing

The cans then travel to the next station where they get gassed. No, that doesn’t mean they have too much to drink. It means the cans are charged with the propellant gas that makes them spray. As you can imagine, this is a very tricky process: the gas is under extreme pressure and evaporates in seconds. So this takes two steps that require split second timing. First, a nozzle shoots a high pressure stream of gas around the valve cup, into the can. Second, a fraction of a second later, the valve cup is pushed down and locked into place. This process involves a device called a crimper that uses little metal fingers to push down onto the valve cup and spread it outwards. This force causes the metal cup to fit tightly against the opening of the can. If the pressure applied during this process is even slightly off, the can won’t seal tightly. And a can that isn’t sealed = a leaky can = a defective product = another return trip to Walmart for you.

This process is also called “under-the-cup-filling” because the propellant is filled before the valve cup is crimped on. There’s another process known as “pressure filling,” where the propellant is filled into the can through the valve stem opening after the valve is crimped into place.

Step 4: Testing

After they’re gassed, the cans take a nice, hot bath. Literally. The conveyor belt runs the cans through a long trough filled with very hot water. As the cans pass through the water bath, people watch for escaping bubbles. Bubbles = gas is escaping = a defect in the can or valve = another trip…ah, never mind, you get the picture.

Step 5: Final Packaging

After their trip to the spa, the cans are dried off by jets of air sort of like those dryers in restrooms except you don’t get to wipe your hands on your pants. Finally, the cans pass through a capping station that places the over cap on top of the package. Then they’re packed into boxes and palletized for shipping.

Whew! That’s much more complicated than just filling a bottle of shampoo! And much more dangerous too. The entire process must be done under special ventilation to avoid buildup of explosive propellant.

So there you have it. Now you should have a pretty good appreciation of how hairsprays and other beauty care aerosols are made.

In the first and second parts of this series, we waxed nostalgic about the history of aerosol products and explained how the packaging works. In Part 3, we talk about the stuff inside the can. There are two basic parts to an aerosol formula: the formula, which is a liquid concentrate, and the propellant which is a gas.

What’s in the formula

The concentrate contains the goodies that makes the product function. If it’s a hair styling product like a hairspray or mousse, the goodies are resins that hold your hair in place. If it’s a breath freshener, the goodies are flavoring agents, and if it’s a depilatory, the goodies are the active ingredients that dissolve your hair. The goodies will vary from product to product, but they give the product its basic functionality. They’re the reason you buy the product in the first place.

In addition to the goodies, the concentrate contains other ingredients like, solvents, fragrance, pH adjusters, anti-corrosion agents, and a bunch of other chemicals that we won`t bore you with right now. All you really need to know is that the concentrate is what makes the product do what`s its supposed to.

What Is A Propellant

Propellant is a general term for any gas that propels the concentrate out of the can. There are several different types of gasses used as propellants, most of which are liquefied gasses. That means when the gas is under pressure it converts to a liquid. If you’ve ever seen a tank of propane gas used on a home BBQ grill, then you know what we’re talking about. If you shake a tank of propane, you can feel it slosh around inside because it’s a liquid. But if you open the valve on the tank: whoosh- the propane comes out as a gas. That’s exactly how an aerosol works. Except in an aerosol the gas is mixed with the product concentrate (remember those goodies!) and the valve on the can is designed to release the product as a spray or a foam.

4 Types of Propellants

1) Propane represents one of the types of gasses used in certain kinds of aerosols. This type of propellant is known as a Hydrocarbon which is also referred to an LPG or Liquid Petroleum Gas. These gasses work very well in aerosols because they’re soluble in alcohol and other solvents used in products like hairspray. However, they are very flammable and they have recently come under fire for contributing to air pollution. In fact, in the US, hydrocarbons are no longer used a primary propellants but they’re still commonly used in other countries.

2) Chlorofluorocarbon (or CFCs) were popular propellants before hydrocarbons. These gasses have low flammability and good solvency, but they were banned from conventional aerosol use in the late 1970s because of fear they were damaging the ozone layer. Once this environmental problem was identified, the aerosol industry rushed to remvoe CFCs.

3) Hydrofluorocarbons (or HFCs) have many of the good properties of CFCs but they don’t affect the ozone layer. If you pick up an aerosol today you know it contains an HFC if it lists 1, 1-difluoroethane or Propellant 152a on the label. HFCs are particularly useful in hair sprays because they allow the creation of formulas without any water. (Water in a hair spray is a bad thing!) So hairsprays containing 152A are the best on the market. Unfortunately, while these propellants are almost technically perfect, they are very expensive so not many companies use them.

4) Dimethyl ether (or DME) is the only propellant that is miscible with water, which allows it to be used in lower cost formulations. While DME is an excellent propellant, adding water to a product like hairspray, can severely affect the way it works. Hairsprays become sticky, slow drying, and make your hair style droop. If you’re shopping for an aerosol hairspray you should really avoid any product that lists water as an ingredient.

Ok, now that you know the fundamentals of aerosol packaging, formulas, and propellants, next time we’ll explain how they all come together to make a finished product. See you back here for Part 4 of Adorable Aerosols!

As we discussed in Part 1 of this series, aerosols are a popular delivery system used in all kinds of household and beauty care products from Air fresheners to Zit creams. But did you realize that aerosols are different from ALL other beauty products because the package itself actually determines the product’s physical properties? In this second part of the Adorable Aerosols series we explain the mechanics of aerosol packaging: the can that holds the product and the valve that controls how the product is dispensed.

Aerosol Cans

If you think about it, an aerosol product is kind of like a bomb. That’s because it contains a pressurized, and potentially flammable, gas. So it`s important that the container is strong enough to withstand increases in pressure. Otherwise the hairspray you left in the back of your car in the middle of August would go Ka-boom! No worries though, because steel and aluminum are used to make aerosols cans extra sturdy. Let’s take a look at each type.

Steel cans are easily recognized because they’re assembled from 3 separate pieces. The body of the can is formed by rolling a sheet of metal into a cylinder. The top and bottom (known as the crown and the base) are formed from separate pieces. All three of these pieces are crimped together to form the can. If you can see the seam down the side of the can and the rim where the top and bottom pieces are attached, you know it’s a steel can.

Aluminum cans, on the other hand, look smooth and sleek because they’re formed by extruding a single slug of aluminum into the desired shape. Both cans are designed with a domed top and inverted bottom to help them invert or bulge if the pressure in the can increases. This allows the can to distort and increase in volume, so it can relieve pressure without bursting.

Steel cans are more commonly used because they’re stronger, cheaper, and easier to process. But aluminum cans are more elegant looking and they are less reactive to water-based products. And both can types are designed for recycling when empty.
Depending on the brand you buy, you can find products in either type of can. Regardless of the whether it`s made from steel or aluminum, the can is sealed with a piece of hardware called a valve.

Valves

Aerosol valves have to do double duty: they have to seal the opening of the can so it doesn’t leak and they have to control how the product is dispensed. The way they accomplish these tasks is really a miracle of modern engineering.

Valves have three main sections: the part you are most familiar with is the button, or actuator that sits on top of the can. This is the part of the valve you push on to release the product. The button has a small opening though which the product comes out. In the case of a spray product, this orifice is very small and the product comes out as a very fine mist. In the case of a mousse or shaving cream, the orifice is a larger spout and the product comes out as a thick foam.

In either case, when you push the button it compresses a spring that opens up a small channel inside the body of the valve. Inside the valve body there are a series of small chambers where the product can mix with the propellant.

The bottom of the valve body is attached to a long, thin straw-like piece of plastic known as a diptube. The diptube extends to the bottom of the container and carries the product from the bottom up to the valve. (have you ever wondered why you have to turn some products upside down to get them to spray properly? That’s because they don’t have a diptube! You have to invert the package so the product inside can reach the valve body.)

All these tiny parts are collected in a steel or aluminum housing, known as the valve cup, that is crimped over the opening of the can after it is filled with the formula and the propellant.

So, when it all comes together, the valve works like this: When the button is pushed, the gas inside the can pushes the formula up through the diptube into the valve body where it is broken up into tiny particles and finally forced out of the small opening on the face of the button. In other words, “Push button, stuff comes out.” Seems simple, but it’s really pretty amazing, huh?

The really astounding part is that these components have measured to a 1/1,000 of an inch or they won`t fit together and the valve won’t function properly. Think about that the next time you’re spritzing your hair.

Ok, now that you’re properly in awe of the miracle of aerosol packaging, you’re ready for a chemistry lesson on what’s inside. Come back to the Beauty Brains for Part 3 of Adorable Aerosols and we’ll tell you about the formulas and propellants used in cosmetic products.

Every time you use a hairspray you’re destroying the atmosphere and speeding up global warming, thus sending human civilization crashing toward extinction.

At least that’s what some people would have you believe. In reality, hairsprays and other aerosols are safe and effective product forms used in thousands of beauty care products worldwide. This is the first installment in our four part series that explains what aerosols are and how they work. (And you can check out The Consumer Aerosol Products Council if you want the truth on aerosols, the ozone hole, and global warming.)

What is an aerosol?

Scientists define an aerosol as a “a self-contained, pressurized spray system designed to dispense various solid, liquid and gas products. This fancy definition really boils down to four basic elements that all aerosols have in common: The formula that the product delivers (e.g., a hairspray or a mousse); a container capable of withstanding high pressures; a propellant that forces the product out of the container; and a valve mechanism that seals the container and controls how the product is dispensed.

By adjusting the chemistry of the product/propellant mixture and by using different types of packaging, aerosols can dispense any thing from liquids, to foaming gels, to powders.

Types of aerosol products

In the context of beauty products, aerosols are used to dispense hairsprays, breath spray, mousses, deodorants, sun tan oils, shaving creams, contact lens sprays, dipilatories, and fragrances to name a few. They`re also used for household products like air fresheners, paints, disinfectants, cook sprays, oven cleaners, insect repellants and hundreds of others. It`s estimated that Americans use more than 1500 different kinds of aerosol products at work and home. They range in size from the giant Sebastion Shaper hairspray size to the tiny purse tote size and everything in between.

History of aerosols

The first aerosols were pesticide sprays developed in the early 1940s to protect soldiers in War II from disease carrying insects. These early aerosol containers consisted of large steel tanks that had to be strapped on the soldiers` backs. (Compare that to the purse-size hairspray you have today!) After the war, the beauty industry realized that this pressurized spray technology could be used to deliver other products and the first aerosol hairspray was born. By the early 1950s, hairsprays, colognes and shaving creams were commonly sold in the U.S. Now, over 50 years later, aerosols are still a popular and effective delivery system with billions of units sold every year.

In the last half century, aerosols have had their ups and downs, however. In the 1970s, a common hair spray solvent, methylene chloride, was banned for health reasons. In the 1970s, CFCs, were banned in most aerosol applications because they were shown to contribute to the hole in the ozone layer. And in the 1990s, US air pollution regulations lead to restrictions on VOC`s (Volatile Organic Compounds) in aerosol products. Despite these setbacks, aerosols continue to be widely used in beauty products.

Over the course of this four part series we`ll talk about the types of packaging used in aerosols (yes, they are recyclable!) as well as the ingredients used to make the products. We`ll even tell you how these things are made! So keep checking the Beauty Brains for the next installment of Adorable Aerosols.