Reusable menstrual underwear is a comfortable and eco-friendly alternative to disposable menstrual products. These underwear are designed to provide leak-proof protection while still allowing your skin to breathe. They are made from a blend of natural and synthetic fabrics, such as cotton, bamboo, and spandex
From Wikipedia
Cloth menstrual pads are cloth pads worn in the underwear to collect menstrual fluid. They are a type of reusable menstrual hygiene product, and are an alternative to disposable sanitary napkins or to menstrual cups. Because they can be reused, they are generally less expensive than disposable pads over time, and reduce the amount of waste produced.