One of the interesting aspects of Sanitary Pads is their ability to act somewhat like a filter. When menstrual fluid comes into contact with the pad's top layer, it starts to absorb quickly. This is due to the capillary action – the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity.

Sanitary pads are designed with a multi-layered structure to efficiently manage menstrual fluid. The top layer of the pad serves as a key element in this process. When menstrual fluid comes into contact with the pad's top layer, it triggers a phenomenon known as capillary action.

Capillary action is the ability of a liquid to flow in narrow spaces without the need for external forces like gravity. In the context of sanitary pads, the capillary action enables rapid absorption of menstrual fluid into the pad. The top layer is often made of materials with high absorbency, such as superabsorbent polymers or cellulose-based materials.

As the fluid is absorbed, it moves through the pad's layers, spreading out and being retained within the core of the pad. This helps in preventing leakage and providing a dry and comfortable experience for the user. The absorbent core is typically made of materials that can hold a significant amount of fluid while maintaining the structural integrity of the pad.

Apart from capillary action, the materials used in sanitary pads are chosen for their softness, comfort, and moisture-wicking properties. These features contribute to the overall effectiveness of the pad in keeping the user dry and preventing potential discomfort during menstruation.