A duct cover for installation on a duct having a known sectional area defined by the duct exterior margin, includes a cover envelop having a body, the body having an open end and an opposed closed end with a center portion extending between the open end and the closed end to define an envelop enclosure, the body being substantially impermeable relative to airborne particulate and moisture, and an elastic member being operably coupled to the body open end and having a relaxed disposition and an expanded disposition, the expanded disposition defining an opening that is area that is greater than the duct sectional area, the elastic member being contractable from the expanded disposition to a duct conforming disposition in compressive sealing engagement with the duct exterior margin. A method of installing a duct cover on a duct is further included.