A disposable diaper is made of roughly a dozen different materials layered together, each with a specific job. The bulk of what you’re holding is a superabsorbent polymer core sandwiched between a soft inner lining, a waterproof outer shell, and a system of elastic and adhesive components that hold it all in place. Here’s what each layer is made of and what it does.
The Absorbent Core
The core is the most important part of any diaper, and it relies on two materials: wood pulp (fluff pulp) and a superabsorbent polymer called sodium polyacrylate. The wood pulp provides structure and helps distribute liquid across the core, while the polymer does the heavy lifting. Sodium polyacrylate is a fine, grain-like powder that can absorb anywhere from 10 to 1,000 times its own weight in liquid, depending on whether it’s absorbing pure water or a salt-containing fluid like urine. When liquid hits the polymer, it gets pulled into the molecular structure and locked into a gel, which is why a wet diaper feels squishy rather than sloshy.
The polymer works because of its chemical structure. Long chains of molecules are lightly cross-linked to each other, creating a net-like framework. Charged groups along the chains attract water molecules and hold them in place. This is also why you sometimes see small clear gel beads on your baby’s skin after a diaper change. Those beads are just the polymer doing its job, and they’re generally considered inert.
The Inner Lining (Topsheet)
The layer that sits against the skin is called the topsheet. Its job is to feel soft, let liquid pass through quickly, and keep the surface feeling dry. Topsheets are typically made from polypropylene, polyethylene, or a blend of the two. Some diapers use viscose (rayon) or cotton fibers instead. These are ultra-thin nonwoven fabrics, meaning the fibers are bonded together without being woven on a loom, which makes them lightweight and breathable.
Between the topsheet and the absorbent core, many diapers include what’s called an acquisition distribution layer. This is a secondary nonwoven sheet that spreads incoming liquid across a wider area of the core rather than letting it pool in one spot. It helps the diaper absorb faster and use more of the core’s capacity.
The Outer Shell (Backsheet)
The backsheet is the waterproof layer that prevents leaks. It’s usually made from polyethylene film, sometimes laminated to a nonwoven polypropylene fabric to give it a cloth-like texture. Older diapers used a solid plastic film that was effective but didn’t breathe well. Most modern diapers use microporous films that block liquid but allow water vapor to escape, reducing heat and moisture buildup against the skin.
Some backsheets also contain calcium carbonate, a mineral filler that makes the film more opaque and can improve its feel. The printed designs you see on the outside of a diaper are applied to this layer using water-based or solvent-based inks.
Elastics, Fasteners, and Adhesives
The stretchy parts of a diaper, around the legs and waist, are made from elastic strands bonded between layers of nonwoven fabric. These strands are typically spandex (also sold under brand names like Lycra), polyurethane, or synthetic rubber. Spandex can stretch up to 400% of its original length before breaking, though diapers use it at less than 300% stretch. Nearly all modern diapers are latex-free, since natural latex can trigger allergic reactions.
The tabs that fasten a diaper closed come in two main types. Premium diapers often use hook-and-loop fasteners (similar to Velcro) that can be opened and resealed. Budget diapers use adhesive tape strips made of polypropylene. Both attach to a smooth landing strip on the front of the diaper, called the frontal tape, which is also polypropylene film secured with adhesive. Hot-melt adhesives, which are applied in a melted state and solidify as they cool, bond many of the internal layers together throughout the diaper.
Additives: Fragrances, Lotions, and Dyes
Some diapers include optional extras that go beyond the basic structure. Scented diapers contain fragrance compounds blended into the core or backsheet. “Fragrance” on a label is an umbrella term that can represent dozens of individual chemical ingredients, which manufacturers treat as trade secrets. Some parents choose fragrance-free diapers to reduce the chance of skin irritation.
Certain diaper brands apply a thin lotion coating to the topsheet, often containing petrolatum (petroleum jelly) or similar barrier ingredients meant to protect skin from moisture. These create a light film that reduces friction and contact with wetness.
The colorful printed designs on the outside, and sometimes the wetness indicator strip that changes color, use pigment-based inks. A study published in the journal Pediatrics linked certain diaper dyes to allergic contact dermatitis in some children, and colorants can potentially contain trace heavy metals. In 2025, New York became the first state to require ingredient labels on baby diapers, partly in response to concerns about undisclosed colorants and other additives.
What About Chemical Residues?
The wood pulp in diapers is bleached to make it white and remove impurities. Two processes are standard today. Elemental Chlorine Free (ECF) bleaching uses chlorine dioxide, while Totally Chlorine Free (TCF) bleaching uses hydrogen peroxide, oxygen, or ozone. Both replaced an older method that used elemental chlorine and produced dioxins as a byproduct. Modern ECF and TCF processes do not create those harmful byproducts, and pulp from either method is considered safe.
Independent testing has detected trace levels of volatile organic compounds (VOCs), phthalates, bisphenols, and heavy metals in some disposable diapers. One study found that the average total VOC level in baby diapers reached 0.094 milligrams per kilogram, a very small concentration. Disposable diapers generally show higher concentrations of these trace chemicals compared to other product types, though the health significance of such low-level skin exposure is still being studied. If minimizing chemical exposure is a priority, looking for diapers labeled fragrance-free, dye-free, and chlorine-free narrows the field considerably.
How Long Diapers Last in a Landfill
The same qualities that make disposable diapers effective, waterproof plastics and synthetic polymers, also make them extremely slow to break down. A conventional disposable diaper takes an estimated 550 years to decompose in a landfill. The polyethylene backsheet, polypropylene fibers, and sodium polyacrylate gel all resist microbial breakdown. The wood pulp component would decompose relatively quickly on its own, but sealed inside plastic in an oxygen-poor landfill environment, even that process stalls. A single baby can go through several thousand diapers before potty training, making diaper waste a meaningful share of household trash.