The quad seal is also known as a four sided seal bag. Side gussets and two panels are joined by 4 vertical seals and the expandable side gussets allow for more volume and to allow the bag to hold its square shape on shelf. They are available with a flat bottom so they can stand on shelf. Or for larger bags, the bottom is closed using a fold under flap so they lay facing up. They can be made of various materials such as plastic, foil and paper and there is usually no back seal so they can be printed on all sides.