The scale of the COVID-19 pandemic and subsequent stain on the global supply chain has led to an acute worldwide shortage of personal protective equipment for healthcare workers. In response, many groups around the world are seeking to develop novel solutions to ensure local supply. N95/P2 respiratory masks are one of the critical components for reducing the spread of COVID-19 and protecting frontline workers. This article reviews the most significant and up-to-date literature around N95/P2 filter fundamentals, manufacturing and reuse, with the aim to serve as an authoritative resource for the development of novel COVID-19 respiratory masks.