How Disposable Diapers Keep Skin Dry Using Porous Plastic Sheets

A 1970 patent by Procter and Gamble describing a specialized plastic top layer for diapers that allows liquid to pass through while keeping the baby's skin feeling dry.

What it covers

This patent describes a hydrophobic, porous plastic film used as the inner layer of a disposable diaper. The material is designed with specific hole patterns that allow urine to quickly pass through into an absorbent core. Because the material is hydrophobic, or water-repelling, it prevents the liquid from flowing back to the surface, effectively separating the moisture from the baby's skin. This mechanism was a fundamental shift from using cloth or non-porous materials that would trap wetness against the skin.

What it doesn't cover

• —Does not cover the absorbent core material itself, only the top layer in contact with the skin.
• —Does not cover non-plastic or fabric-based top layers that rely on absorption rather than fluid transport through holes.
• —Does not cover diapers that do not use a hydrophobic material to prevent liquid back-flow.

The clever bit

The innovation lies in using a hydrophobic material with specifically sized apertures that exploit surface tension to let liquid move in one direction only, effectively creating a one-way valve for moisture.

Why it matters

This invention was a cornerstone in the development of the modern disposable diaper industry. By solving the problem of 'wet-back'—where moisture returns to the skin surface—it enabled the mass-market success of brands like Pampers. It transformed diapers from a simple absorbent pad into a sophisticated engineered product.

Real-world examples

• 1.Pampers disposable diapers
• 2.Generic disposable diaper top sheets