Why Do Some Sanitary Napkins Absorb Slowly? The Technical Know-How of the Absorbent Core

2026-04-13

Why Do Some Sanitary Napkins Absorb Slowly? The Technical Know-How of the Absorbent Core

⭐ Slow Absorption Comes Down to Core Structure

Whether a sanitary napkin absorbs liquid quickly depends not so much on the top sheet but on the absorbent core inside. The core generally consists of two layers: the acquisition/distribution layer (ADL) and the retention layer.

The ADL quickly pulls liquid into the core, preventing it from pooling on the surface. The retention layer spreads and locks the liquid away, preventing backflow. If the ADL fibers are too dense or too sparse, liquid will linger on the surface and struggle to penetrate. That is the direct cause of slow absorption.

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⭐Core Material Ratio Determines Speed and Dryness

Most mainstream sanitary napkin cores use a mixture of super absorbent polymer (SAP) and fluffy wood pulp. SAP locks liquid in, while wood pulp helps with liquid distribution and wicking.

Too much SAP: Absorption may be fast but too localized. The surface stays dry, but the core swells unevenly, increasing the risk of side leakage.

Too much wood pulp: Liquid spreads quickly but isn't well locked in – pressure causes backflow, the surface feels wet, and skin irritation can occur.

⭐Core Forming Process Affects Uniformity

The core is not simply mixed together. On the production line, a specialized forming head lays down a uniform web of fibers and SAP. If the distribution is uneven – some areas heavy in SAP and light in pulp, others heavy in pulp and light in SAP – absorption suffers.

Our factory uses an airlaid forming process, where fibers are dispersed in an air stream before settling. This is more uniform than traditional carding methods, resulting in a consistent core thickness and faster absorption.