What Are Disposable Diapers Made Of?

Disposable diapers are made of different layers of materials stacked together. If you name the layers from inside (the part touching your baby’s butt) towards the outside (the waterproof outer shell) in order of 1,2, and 3 then you have the following:

  1. Top sheet (the fabric looking thing your baby’s butt sits on all day)
  2. Absorbent core (it keeps the pee away from you baby deep inside the diaper)
  3. Back sheet (waterproof so that when you hold your baby in your arms, there won’t be sludges oozing through the diaper onto your favorite shirt)

No matter what kind of disposable diapers you buy, these three layers are basically made with the same four ingredients. They are:

  • Paper
  • Plastic
  • Super absorbent polymer (SAP)
  • Glue (hot melt)

Diapers Are Paper Towels????

This might confuse you at first because you probably don’t understand how paper plays a role in diapering. Believe it or not, paper plays a very important role in your diapers. Paper have two functions in diapers. First function is that they absorb part of the moisture that your baby pees or poops out. In a sense, it is similar to how paper towels works.

Second function is that they quickly spread out the pee and sends it towards the diaper core. This is why your baby’s butt will remain dry for hours because the paper directs the moisture away from your baby’s butt so quickly, that it doesn’t have a chance to stay. This is a fairly important function because this function dramatically reduces diaper rashes.

Why Doesn’t Paper Feel Like Paper In Diapers?

The paper you see in diapers are not your ordinary tissue paper. The raw materials have been specially processed into something known as airlaid paper. This is the inner fluffy part of your diaper. If you ever see air laid paper freshly made, you would probably think that it is cotton instead of paper. Of course, you normally don’t see diaper manufacturers naming their ingredients air laid paper. What they commonly name them on their boxes are pulp.

Here’s a YouTube video of what air laid paper looks like:

The interesting thing about airlaid paper is that it does not scratch your baby’s skin. It is soft, fluffy, bulky, tough and can be reused after being wet. The airlaid paper was created by someone named Karl Kroyer in the 1980’s which is pretty darn recent.

It’s only been roughly forty years ago. In other words, your great grand parents probably didn’t have much chance to try it on your parents.

Air laid papers are also used in many other areas of your life like paper towels, and baby wipes due to their toughness, and re-usability.

What Is Airlaid Paper Made Of?

This paper can be made from many different ingredients like wood, bamboo, or hemp.  Parents in general tend to look down on wood because you have to cut down trees to make it. The recent trend supports bamboo and hemp because they supposedly grow back faster and are ready in bulk. The general belief is that using bamboo and hemp make the paper pulp is more environmentally friendly.

Is It More Eco Friendly To Use Bamboo And Hemp?

However, that is not really true. I don’t deny the fact that cutting down trees is bad for the environment. However, if you do it in a controlled matter where you plant more tree supplies than you cut down, like getting FSC certification for example, then there’s not really a problem.

On the other hand, if the whole world relies on bamboo or hemp in bulk, things can get pretty dangerous for planet earth. I will talk more about this in another article. Instead of going into the details, the short answer as to why bamboo and hemp are not better renewable resources is because of the land and water they consume.

This is why none of the ingredients mentioned above are more environmentally friendly than the others.

Why Use Plants To Make Diapers In The First Place?

All plants have cellulose which is like a huge bundle of miniature straws. When water comes in contact with it, capillary action allows these straws to suck it all up. This is why water from the roots of tree can reach the highest tree trunks that are hundreds of feet high. There’s also the help from proton-ion exchange pump at the roots, but we’ll talk about that some other time.

Of course no matter how absorbent paper is, paper is still paper. It can take away water, but it can not imprison the water and prevent leakage. It will eventually leak back out. Have you ever tried holding a wet piece of  paper towel on your hands? If you hold it long enough, your hands will get wet.

This is why that if diapers were only made of paper, your baby will definitely get a diaper rash, because she sits on it all day.  To prevent this, diaper companies have invented a top sheet for your baby to sit on.

What Is The Top Sheet Made Of?

There’s a reason why your baby can keep her butt dry for four hours straight while wearing pampers swaddlers. The reason is because she is sitting on a plastic top sheet that blocks off the wet paper that I mentioned earlier.

Wait a minute? Plastic?

That doesn’t make sense, because plastic is waterproof.  If the top sheet was made of plastic, then there’s no way that moisture can successfully pass through it to reach the absorbent core. If you have a regular block of plastic, then yes, that is true. However, the top sheets for disposable diapers are specially modified plastic.

The top sheet you see in diapers has been modified into something known as a nonwoven fabric. It might sound unbelievable that plastic can be turned into fabric like. However, you already use plenty of this stuff in your everyday life. If you check your shirts, jackets, or pants label properly you will then notice that one of the ingredients are polyester which is basically a form of plastic. This is also why recycled plastic bottles can actually be made into clothing.

Unlike the polyester clothing you wear, diaper top sheets are usually made of polypropylene which is a fancy name of a thermoplastic created as byproduct of crude oil extraction. This stuff is normally waterproof because it is hydrophobic (derived from a oil substance). However, due to flattening, stretching, needle punching, or whatever methods a manufacturer has decided to use, air gaps (microscopic holes) are formed.

In other words, the material itself is still water repellent, but the air gaps are what allows water to flow from your baby’s butt to the absorbent core of the diaper. The interesting thing is that due to the fact that polypropylene can be made into such small fibers (microfibers), the capillary force is stronger than cotton fibers, and therefore water gets pulled in better than cotton. This is the reason why cloth diapers can never beat disposable diapers when it comes to absorbing pee and keeping your baby’s butt dry.

The modified top sheet sounds cool and all. However, if water can go in one way, then it can come back through the same channel right? Theoretically that is only true if your diapers only rely on paper to absorb all the fluids.

If that was the case, the fluid will eventually squeeze right back out and ferment on your baby’s butt. Fortunately, this doesn’t happen, because the diaper core has a special substance that keeps the diaper dry for couple of hours.

The Absorbent Core

So far you learned that the top sheet (the layer touching your baby’s butt) does the job of redirecting the wetness towards the core, so what is the core made of? In the past, diaper manufacturers have made many different designs that failed at keeping a baby’s bottom dry. In the end they came up with the idea of making the perfect absorbent core by layering different amounts of air laid paper (the pulp) with SAP sprinkled in the middle.

In terms of locking away the moisture, the super absorbent polymer (SAP) is the main pillar of all disposable diapers. It doesn’t matter whether the disposable diaper you use is considered environmentally friendly or not. They all need SAP in order to keep your baby from having diaper rashes. SAP are also the beads you see when your baby’s diaper explodes from having too much pee in it.

The paper pulp mentioned earlier does part of the absorption, but its absorption capabilities are very limited. What the pulp truly does is that it transfers the moisture (pee) to the SAP. As mentioned earlier, paper pulp is like a thousand of tiny straws. You can think of these straws like mini tunnels that draws liquid to the most moisture hungry destination, which is the SAP.

This is why something like wood, bamboo, or hemp are used because plants have cellulose that are natural straws. It is the same reason why plants have the ability to draw in moisture from the soil. They literally suck it up.

SAP is so powerful, it can lock in moisture that is around 300 times its weight. However, as mentioned in a different article, this gets reduced to 80 times its own weight, because urine has salt in it, which can compete with SAP for moisture. In other words, SAP absorbs distilled water better than salt water (which is what our pee basically is).

SAP also has other applications like:

  • keeping electrical wires dry by mixing into the insulating material
  • Thickening hair gel because because it is thick and slippery when wet
  • As a part of ice packs
  • Food processing to dry out moisture and prevent bacteria growth
  • As mentioned in a different article, you can use it to keep your plants watered (the original plan of inventing SAP is for the sake of agriculture)

What is SAP made of?

The traditional method of making sodium polyacrylate is to combine acrylic acid with sodium hydroxide (lye). Lye might sounds scary because it is toxic, but it is the ingredient used to make 99% of the soaps you use.  As for acrylic acid, it is made from propene. Propene is made from cracking crude oil. The new method is to add plant starch to this formula so that the SAP is easier to break down after being disposed of.

Is SAP safe?

SAP is biologically inert. In other words, it won’t burn or give you cancer. However, if you inhale SAP powder then it can irritate your lungs quite a bit. If you swallowed some by accident, then drink lots of water to flush it back out, because it will rapidly suck up the water in your system.

Of course, if you swallowed a lot of SAP then that can be pretty dangerous, because it can dry you up and clog up your system because it can swell. Go to an emergency room right away if that is the case. However, if the SAP has already exploded from the diaper due to having too much wetness, then it should be even safer because it can not absorb any more fluids.

So now you learned how the diaper core keeps moisture locked into the core of the diaper. This keeps your baby’s butt dry during the day. However, how does diapers prevent pee from leaking out onto the baby clothes?


The Back Sheet

petroleum oil

Just like the top sheet, the back sheet is also made of plastic. However, instead of polypropylene, it is made of polyethylene. Unlike polypropylene, polyethylene is made intentionally by using different treatments of crude oil like cracking for example.

It takes a cup of crude oil just to make enough polyethylene for one diaper. The cool thing about polyethylene is that it can keep moisture locked in so that it does not leak through diaper. In other words, it waterproofs the diaper exterior. What is very interesting is that polyethylene is made to intentionally allow water vapor to leave and pass through the diaper.

There are three purposes to doing this. First purpose is to make the diaper breathable so that it reduces the chances of diaper rashes. Second purpose is to allow heat to escape the diaper to minimize germ growth.

As you know, germs love warmth and wetness. The third purpose to allow stinky poop odor to escape and reach your nose. This might sound disgusting, but it is actually an ingenius idea to warn parents of poop. Poop has a lot of germs, so a poopy diaper should be changed as soon as possible.

How Does A Plastic Back Sheet Become Breathable?

Just like polypropylene top sheet, the polyethylene back sheet has been modified with stretching so that micro-holes can be formed to produce this breathable feature.

Is Polyethylene Used Anywhere Else?

Polyethylene is nontoxic when it is in solid form (unless you intentionally melt and burn it). It serves a lot of household needs like for example:

  • Making the plastic wraps for your leftovers
  • Waterproofing cardboard juice bottles and keeping it together
  • Water bottles you drink with
  • Stitches to close open wounds

Polyproylene vs Polyethylene

You might be wondering why the back sheet and the top sheets are made of two different forms of plastic even though companies could have made it with one type of plastic instead. Personally, I do not know why.

However, polyethylene tends to be stretchier than polypropylene. This is rather important because the backsheet can often be readjusted several times before parents like you and me and wrap the diaper correctly. This is especially true if your baby is struggling and playing tug of war with you during a diaper change.

Polypropylene is inflexible and tougher so it can be made into a fabric that doesn’t require stretching, as mentioned earlier, and the heat from your baby’s body heat most likely won’t affect it because it has a higher melting point than polyethylene

Hot Melt

You have the top sheet, absorbent core, and the back sheet. Finally, to combine all of that together to look like a single diaper, you add one more ingredient, which is the hot melt. Hot melt might sound like something you can order on top of a cheeseburger, but it is actually a fancy name for a type of glue.

You probably have seen this type of glue before. They come in a form of cylindrical glue sticks that has almost the same dimensions a pencil. A glue gun that is plugged to an electrical outlet is required to melt these glue sticks. Of course, a diaper factory will use other methods to spray this hot melt on disposable diapers to stack the layers together. This stuff is nontoxic unless you decide to burn your diapers as mentioned earlier.