Filain is a former commune in the Aisne department in Hauts-de-France in northern France. It was merged with Pargny-Filain to form Pargny-et …Filain is a former commune in the Aisne department in Hauts-de-France in northern France. It was merged with Pargny-Filain to form Pargny-et-Filain on 1 January 2025. The river Ailette forms all of the commune's northern border.