How are diapers made? What are diapers made of? | A Parent’s Guide

As a nerd, I’ve often wondered- how are diapers made, and what are disposable diapers made of?

The internet is full of fantastic resources on every aspect of these questions from what ingredients are in diapers, to what each component contributes to the diaper’s properties. 

First, we’ll start with what are diapers made of, then get into how disposable diapers are made.

how are diapers made and what are they made of - discover the science and chemistry

What are diapers made of?

Disposable diapers use a variety of different materials. In a way, they’re like a sandwich. Let’s look at the different layers of diapers, what they are made of, and why they’re important to have in a diaper! 

I’ve used a number of different sources to compile all this data, and reference them throughout the post and at the end of the article.

Absorbent Core

First, we’ll start with the absorbent core, as diaper companies like Pampers and Seventh Generation call it, is the fluffy stuff inside the diaper that soaks up liquids. It consists of one to two different materials, depending on which brand of diapers you buy.

Super Absorbent Polymer (also known as Sodium Polyacrylate or SPA)

Image courtesy of Amazon

Next, let’s get into what the absorbent core is made of. Super Absorbent Polymer, also known as the chemical sodium polyacrylate, or SPA, can absorb ten to one hundred times its weight in water! Before SPA, diaper companies uses materials like cellulose and cotton, which only absorb up to about 20 times their weight in water. Using SPA allows disposable diaper manufacturers to make diapers lighter weight and lessen their carbon footprint. 

Other chemicals that absorb moisture release the water when they’re squeezed. But not SPA! Your baby can roll around in a wet diaper, sleep, or crawl, and the SPA keeps the moisture locked in away from their body. 

Absorbent products like sanitary napkins, puppy pee pads, and even instant snow all use SPA.

In a diaper, the SPA is not in contact with your baby’s skin. The diaper has several layers in between. Even so, SPA is nontoxic and isn’t harmful to skin. In fact, it’s even used in some products like lotions, ice cream juice, and bread where it comes in contact with the skin or is even eaten [Source]!

Wood Fluff Pulp

what are diapers made of- wood fluff pulp courtesy of
Wood fluff pulp, courtesy of

Diapers use a material known as wood fluff pulp to also absorb moisture. Kotex first developed it to use in sanitary napkins. And diapers made before the 1980s used fluff pulp for all their absorption. 

These days, fluff pulp keeps the absorbent part of the diaper strong. The super absorbent polymer (see above) does the heavy lifting when it comes to picking up moisture. Fluff pulp holds together when wet, so a diaper won’t completely turn to a mushy mess when it gets wet! 

And fluff pulp is part of wood and paper processing. Paper companies use softwood trees to make fluff pulp, which grow more quickly than hardwoods. Their wood, as the name implies, is also softer and easier to process into the fluffy, cottony fluff pulp. [Source: American Forest and Paper Association]

Absorbent Top Sheet

You’ve probably noticed that the inside of most diapers have a white rectangle (or occasionally a different color) on the inside, where the diaper is closest to the baby’s genitals. That’s the top sheet. Its job is to quickly soak up moisture and keep it away from the baby’s very sensitive skin. 

The absorbent top sheet is often made of polypropylene, polyethylene and polyester. Many diapers use hydrophilic polypropylene in the top sheet to suck up moisture and keep the baby’s skin dry. 

The food industry uses polypropylene for lots of things, like the lid of Tic-Tac containers, Rubbermaid containers, as well as medical equipment, such as pharmacy prescription bottles. 

Outer Cover 

The diaper’s outer cover contains any mess and is waterproof to keep the baby’s clothes and bedding from getting wet. It also has to stand up to a baby crawling, scooting, and rolling around. The outer cover, like the top sheet, is often made of polyethylene and polypropylene. 

In some cases, the outer cover is made of Lycra or Spandex- the same material used in clothing. 

How does the diaper wetness indicator work?

Many brands of diapers have wetness indicators to let parents know when to change the diaper! The yellow stripe turns blue when the baby pees.

Most diapers use a pH indicator that is yellow and turns blue. The most common chemical is bromophenol blue. It’s yellow when the diaper is dry, but turns blue when the diaper’s pH changes from the presence of urine. Other products and industries use it to monitor chemical processes and reactions where a pH change occurs. [Source]

Diaper Prints and Patterns

To get those cute designs, diaper companies use pigments and dyes. They might include the diaper size, indicators to show where to fasten the diaper and when it’s time to go up a size, or cute animals or cartoon characters. 

Many parents are concerned about the safety of dyes and pigments in contact with their child’s skin. Fortunately, most diaper manufacturers use pigments, which are much safer. Pigments have large particle sizes, which means they won’t be absorbed through the skin. The cosmetics industry uses these pigments too. They are safe when in contact with the skin for a long time.

Fasteners, Waist Elastic, and Leg Cuffs

As you probably guessed, the fastener tabs hold the diaper closed.  

The waist elastic is the waistband. But not every diaper has an elastic waistband (for example, Huggies and Seventh Generation do, and Pampers does not).

And the leg cuffs are the elastic gussets that stick out around your baby’s legs. The extra material helps prevent leaking around the legs!

The diaper fasteners and leg cuffs are made of polypropylene and elastic. These are the same materials commonly used in clothing. 

Image of hook and loop fasteners- the fasteners on diapers are the same technology as Velcro and similar products you use every day. Image courtesy of Amazon

Diapers have hook and loop fasteners just like the ones you see everywhere. You’ve probably heard of these before by the trade name Velcro.

Seams and Joints

Now that we have all these different diaper parts, how do we hold them together? With adhesives! 

There are many types of adhesives out there. Diaper companies use hot melt adhesives. That means they heat up the adhesive and use it to stick parts of the diaper together. Think of it like a hot glue gun. When it’s hot, the glue is sticky and will adhere things together. And once the glue cools, it’s not sticky anymore. This is a great solution for diapers so that there are no sticky parts after it’s cool! 

To keep a baby’s skin safe, the adhesives are in between layers of the diaper. That is to say, they just touch parts of the diaper, and not your baby.

Chemicals in diapers

Today’s disposable diapers are free of parabens, latex, rubber, and harmful pigments and dyes. Diapers use many chemicals. They all undergo rigorous safety testing.

  • Absorbent core: super absorbent polymer and wood fluff pulp
  • Top sheet: polypropylene 
  • Outer cover: polypropylene 
  • Wetness indicator: bromophenol blue
  • Diaper prints: pigments and dyes
  • Fasteners, Waist Elastic, and Leg Cuffs: elastic, polypropylene, and Velcro
  • Seams and joints: hot melt adhesives 

Properties of disposable diapers 

Disposable diapers have several important properties:

  • Absorbency: to soak up urine and keep it away from a baby’s skin
  • Flexibility: to snugly fit against the baby and move when the baby moves
  • Softness: to feel soft and smooth against the baby’s skin
  • Nontoxic: all diapers undergo stringent testing to make sure they are safe
  • Hypoallergenic: today’s diapers are free of latex, rubber, and harmful pigments and dyes. Certain brands are free of other components too.

How are diapers made? 

Here’s a fantastic look into how diapers are made, by How It’s Made

How is the diaper top sheet made? 

As we learned earlier, the diaper top sheet quickly pulls moisture away from the baby’s skin into the absorbent core. And it’s typically made of polypropylene. 

To make the diaper top sheet, hot, melted polypropylene plastic is pushed or extruded through tiny holes to turn it into fibers. Think of it like the Play-Doh spaghetti kit you had as a kid

Extruding plastics like those used in diapers is very similar to using a noodle maker or a Play-Doh noodle maker! Image courtesy of Amazon.

Once the polypropylene fibers are extruded, they fall onto a conveyor belt. Then they go through heated rollers that squish and flatten the polypropylene into a fabric-like sheet. 

How is the diaper back sheet made? 

Just like the polypropylene top sheet, the polyethylene diaper back sheet is made of nonwoven polyethylene. And like the polypropylene, it’s processed in the same way. Fibers of molten polyethylene are extruded and then flattened into a nonwoven fabric.

How is the diaper absorbent pad made?

Picture this: a conveyor belt with holes in it passes through a tunnel called a forming chamber. While it’s going through the tunnel, nozzles spray the super absorbent polymer and fluff pulp onto it at certain points. Vacuum suction on the bottom of the conveyor belt sucks the absorbent materials into a flat pad. Basically, alternating layers of super absorbent polymer and fluff get laid down in a sandwich to make the pad. Finally, the pad goes through a set of rollers that removes a little bit of the top of the absorbent pad to make sure it’s a consistent thickness.

Another thing that I find fascinating (and most people probably don’t) is that companies don’t make these diaper pads one at a time. They make it in a huge sheet of material. Later in the process, it will get cut up into smaller pieces to make individual diapers.

How are the diapers put together? 

Now we have three layers. The top sheet, absorbent pad, and the back sheet. How do we put all these layers together to make a diaper?

First, all three materials are cut down into the right width to make a diaper.

Next, elastic is adhered to the back sheet to form the leg cuffs, and in some cases, the elastic waistband. 

Next, a roll of back sheet, a roll of absorbent pad, and a roll of top sheet are all unrolled on top of each other like a sandwich. Adhesives are put between the layers, and heat is used to stick all three layers together. Any prints and diaper tabs are put on. Finally, machines cut each diaper to size, fold, and pack each diaper for shipment.

Sources: How are Diapers Made?

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