Stand & fill. Expandable bottom. Stronger seal than Ziploc bags (when shaken). Patented Maxlock: Track design for an extra strong seal. Click Closed: So you know it's closed. Zipping sound: Indicates the seal is secure. Expandable Bottom: Easier to stand & fill. When communicating about this particular product, please include end flap with the embossed numbers, or laser printed white numbers and the UPC bar code located on this panel.