Abstract: A bag for popping popcorn in a microwave oven has substantially rectangular front and back walls and gusseted side walls joining the opposite side edges of the front and back walls. The gusseted side walls each has a medial gusset fold, defining a pair of gusset panels joined along longitudinal folds to the adjacent side edges of the respective front and back walls. When the bag is folded flat, the gusset panels and medial gusset folds lie between the front and back walls, with the medial gusset folds of the opposite gusseted side walls normally spaced from one another. Transverse bands of adhesive extend across the top and bottom ends of the bag interior surface to adhesively attach the gusset panels to the respective front and back walls, forming bag end closures.