A disposable diaper looks simple from the outside. Inside it's a small engineered system — six distinct material layers, each doing a specific job, assembled from a mix of well-studied and largely unregulated inputs. Understanding what those layers are, and what gets added to them, is useful groundwork before evaluating any brand's label claims.
The absorbent core
The center of a disposable diaper is two materials working together.
Fluff pulp is processed wood fiber — typically softwood — bleached and milled into a fibrous mat. Its job is to pull liquid away from the skin and distribute it into the layer below. The pulp chemistry itself is low-concern; the concern is the bleaching step (covered below).
Sodium polyacrylate (SAP) is the superabsorbent polymer responsible for the gel-like material inside a wet diaper. SAP can hold 300–500 times its weight in liquid and retain it as a gel under mechanical pressure — which is why diapers stay dry to the touch after saturation. SAP was introduced into diapers in the 1980s. Because it was a new synthetic material added to a product in intimate contact with infant skin, it was studied extensively. Regulatory assessments in the U.S. and EU have not identified systemic safety concerns for SAP in normal diaper use; the polymer molecule is too large to cross intact skin. The one documented concern — respiratory exposure to loose SAP dust — is a manufacturing context issue, not a wearing one.
The layer touching skin: top sheet
The inner surface you see — soft, white, with that slight texture — is almost always a polypropylene (PP) nonwoven fabric. Polypropylene is a plastic, but in nonwoven fiber form it's considered chemically inert at skin-contact temperatures. It doesn't require plasticizers, doesn't contain bisphenols, and isn't associated with phthalate migration in finished fiber form.
What's applied to the PP top sheet is a different question. Lotions, fragrance, and dyes are sometimes applied as finishing treatments, and none are subject to ingredient-disclosure requirements for diapers in the U.S.
Some brands use polyester (PET) nonwoven instead. Polyester can shed microplastic fibers over repeated use cycles, and it requires antimony trioxide as a production catalyst, with trace residuals possible in finished fiber. Neither the FDA nor the CPSC requires disclosure of either.
The waterproof outer layer: back sheet
The diaper's outer surface is a thin polyethylene (PE) film. PE's job is waterproofing: keeping liquid from passing outward. In its cured film form, PE is chemically inert and well-characterized. The additives applied on top — print inks, dyes for waistband graphics — are less regulated.
Some manufacturers offer breathable back sheets: PE films with micropores, or PP/PE laminates that allow vapor transmission while blocking liquid. These are legitimate material engineering choices and the breathability claims are generally accurate.
Elastic components
Leg cuffs and the waistband use synthetic rubber — typically spandex (polyurethane-based) or a thermoplastic elastomer (TPE). Elastic sits against skin continuously at the leg openings, which is also where diaper rash most often develops.
Latex has been largely phased out of mainstream disposable diapers because of the documented allergy risk. Most brands now use only synthetic rubber. If latex sensitivity is a concern, the brand's materials FAQ or packaging usually clarifies.
Fragrance and dyes
Fragrance may be added to the top sheet, the pulp core, or the outer cover — primarily for odor masking. "Fragrance" as a single declared ingredient can represent dozens of underlying compounds. Neither the FDA nor the CPSC requires constituent disclosure on diaper packaging.
The American Academy of Dermatology and the American Academy of Pediatrics have both recommended avoiding added fragrance in products used on infants. Diaper rash has been linked to fragrance exposure in observational studies, though causation is difficult to isolate from other variables (wetness, fit, frequency of changes).
Dyes are used for waistband graphics, brand logos, and wetness indicators. These colorants contact skin at leg openings and the waistband, particularly in smaller sizes where the diaper covers a larger proportion of the body surface. There is no U.S. regulatory standard for colorants in diapers and no required disclosure.
Bleaching and dioxins
Fluff pulp is bleached to make it white and reduce bacterial contamination. The original industrial process used elemental chlorine, which produces dioxins and furans as byproducts. Dioxins are persistent organic pollutants; EPA classifies dioxin as likely carcinogenic to humans, with no established safe threshold at low doses.
Starting in the early 1990s — in response to FDA concern and market pressure — most manufacturers shifted to:
- ECF (Elemental Chlorine Free) — replaces elemental chlorine with chlorine dioxide. Substantially lower dioxin formation, but not zero.
- TCF (Totally Chlorine Free) — uses ozone, hydrogen peroxide, or enzymatic processes. Eliminates the dioxin pathway entirely.
Most major brands now use ECF or TCF bleaching. Many independent brands have moved to TCF or unbleached pulp. The label doesn't always specify which; the brand's FAQ or materials documentation usually does. TCF eliminates the source concern entirely.
What "hypoallergenic" and "fragrance-free" actually mean
These are the two claims parents most commonly use to filter diapers. Neither is regulated in a way that guarantees what the label implies.
"Hypoallergenic" has no legal definition under U.S. law. The FDA attempted to create a regulatory standard in 1974 and was blocked by industry litigation; the standard has never been established. A diaper labeled hypoallergenic may have undergone internal irritancy testing (self-reported by the manufacturer) or may have had nothing done at all. No required test protocol exists; no agency enforces the claim.
"Fragrance-free" typically means the manufacturer did not add fragrance as a declared ingredient. It does not mean the product is free of fragrance-like compounds. Processing aids, odor maskers, and residual manufacturing chemicals are not classified as "fragrance" even when they contribute an odor. "Fragrance-free" says nothing about dyes, bleach process, or elastic additives.
"Unscented" is weaker still: it describes the end-product smell, not the ingredient list. A product can carry masking fragrance to neutralize another scent and still be legally unscented. See our Fragrance-Free vs. Unscented explainer for the full breakdown.
What the certifications actually cover
The one certification with meaningful independent teeth for diapers is OEKO-TEX Standard 100 Class I. OEKO-TEX 100 tests the finished product against a list of hundreds of substances — including formaldehyde, heavy metals, pesticide residuals, phthalates, restricted azo dyes, and EU-listed fragrance allergens. Class I is the most stringent tier, required for products in prolonged direct contact with baby skin.
What Class I testing verifies that label claims don't:
- Fragrance allergens listed in EU Regulation 1223/2009 (75+ named compounds)
- Azo dyes that cleave to release carcinogenic arylamines
- Heavy metals in colorants, prints, and surface treatments
- pH range appropriate for infant skin
- Formaldehyde from textile finishing agents
The certification requires third-party lab testing by an OEKO-TEX accredited institute, not self-reporting. Brands must re-test regularly. Certificates are verifiable on the OEKO-TEX label check.
MADE SAFE is a broader certification that also covers diapers and screens for a longer list of chemicals of concern. It's less common in the diaper category but more comprehensive in scope.
Most babies use conventional diapers without incident. The goal here isn't alarm — it's clarity about which label claims are backed by regulation and which aren't, and what independent testing can verify that packaging doesn't.
If you want to apply these criteria to a shortlist: our PFAS-free disposable diaper guide walks through five brands that passed testing. Every product on it has been screened against our vetting criteria.
Cover image: Boko Shots via Pexels (Pexels License) — source.
