The duo, a French product designer and a Harvard University biomedical engineer, unearthed NASA research from the 1980s on plants that absorb chemicals through their leaves and roots. Philodendra, for instance, soak up formaldehyde much as they do carbon dioxide. But plants can clean only the air that touches them. To quickly and efficiently clean a whole room, LeHanneur constructed a container that moves as much air as possible around the entire plant. A fan blows breezes around the leaves, and a second fan sucks air through a hole in the soil. Microbes on the plant's roots metabolize more toxins than the leaves do, and the soil works like a traditional charcoal filter to capture even more. Underneath the soil, a tray of water produces humidity that keeps the plant moist and traps additional toxic molecules. A vent on the side releases fresh air into the room. In early trials, the device reduced a test chamber's formaldehyde concentration by 80 percent in one hour.