Abstract: A reusable mailer bag includes front, rear, first side, second side, and bottom panels which include interior surfaces that define a carrying volume that has an opening which is opposite the bottom panel. The mailer bag also includes a flap and a first side extension. The flap is configured to extend across the opening to close the carrying volume during shipping. The flap includes a first end portion that is attached to the rear panel and a second end portion that is configured to secure to the front panel. The first side extension extends from a first edge of the second end portion of the flap that is adjacent the first side panel. The first side extension is configured to extend around the first side panel and to secure to the rear panel when the second end portion is secured to the front panel.