A sanitary pad is designed for the management of menstrual fluid. Its primary function is to capture and retain fluid away from the body, allowing individuals to maintain hygiene and comfort during menstruation. The technology relies on a sophisticated composite of materials working in concert to ensure rapid absorption and secure containment.
The Layered Structure of a Pad
The effectiveness of a sanitary pad begins with its multi-layered design, which functions like a one-way street for liquid. The layer that makes contact with the skin is the topsheet, typically made from a non-woven fabric of polyethylene or polypropylene fibers. This material is engineered to be highly permeable, allowing fluid to pass through quickly while maintaining a dry feel against the skin. By wicking moisture away, the topsheet minimizes skin exposure to wetness, reducing discomfort and irritation.
Beneath the topsheet is the absorbent core, the product’s main storage reservoir. This core is a blend of fibrous material, often cellulose or wood pulp, mixed with specialized synthetic polymers. The fibrous pulp acts as a structural scaffold, creating a matrix that helps draw and distribute the fluid across the pad’s length.
The final protective layer is the backsheet, an impermeable barrier commonly made from a thin polyethylene film. This plastic layer prevents the absorbed fluid from leaking out onto clothing, providing the necessary protection against staining. An adhesive strip is applied to the outer surface of the backsheet, securing the pad to the underwear to ensure correct positioning during movement.
The Mechanism of Super Absorbent Materials
The core’s capacity to lock away large volumes of liquid is due to Super Absorbent Polymers (SAPs). These materials are typically small, granular particles, most commonly the synthetic polymer sodium polyacrylate. Sodium polyacrylate has a molecular structure that allows it to absorb liquids through a process involving osmosis and ion exchange.
When the dry granules encounter fluid, the water molecules are quickly drawn into the polymer network, causing the material to swell dramatically. A single gram of this material can absorb hundreds of times its own weight in pure water, transforming the liquid into a stable, immobilized gel. Gel formation traps the fluid and prevents its release, even when pressure is applied to the pad.
The cellulose fibers initiate fluid transfer via capillary action, pulling liquid away from the topsheet and distributing it to the SAP particles. This rapid movement and distribution ensure that the entire core is used efficiently and prevents “gel blocking,” where localized swelling inhibits fluid penetration to the deeper layers. By quickly converting the liquid into a gel, SAPs maintain a dry surface environment, benefiting user comfort and skin health.
Selecting the Appropriate Absorbency Level
Manufacturers categorize pads using absorbency ratings—light, regular, heavy, and overnight—which relate directly to the composition of the absorbent core. These ratings are determined by the quantity and concentration of the fluff pulp and Super Absorbent Polymers within the pad. Pads rated for heavy or overnight use contain a higher proportion of SAPs to maximize fluid retention capacity, allowing for longer wear times.
The physical design also contributes to effectiveness for different flow volumes. Pads designed for greater absorbency are often longer and wider, providing increased coverage area and a larger surface for fluid capture. Features like “wings,” which fold around the underwear, maximize security and prevent side leaks during movement. Choosing the appropriate absorbency level ensures the product’s capacity aligns with the user’s menstrual flow.