"Every month, millions of girls and women around the world miss school and work during their periods because they don't have access to menstrual products such as pads or tampons. In 2008, Celeste Mergens was working with an overcrowded orphanage on the outskirts of Nairobi, Kenya, when she learned that menstruating girls there sat on cardboard in their rooms for several days each month. This set into motion a seemingly simple idea-combining a washable,...