The Department of Mechanical Engineering of The Hong Kong Polytechnic University (PolyU) has recently developed an electrostatically charged nanofiber filter with multiple separator layers, which can capture pollutant particles that are below 100 nm in diameter (covering the most common airborne nano-particles and viruses). The novel nanofiber filter demonstrates better performance in terms of breathability, filtration efficiency (10 percent higher than the conventional electret microfiber filter), and shelf life (up to 90 days).