A gallon-size Ziploc bag is a large, transparent plastic storage bag typically measuring approximately 10-9/16 inches by 10-3/4 inches (26.8 cm x 27.3 cm). The bag is made from a durable, food-grade polyethylene plastic that is thicker than a standard sandwich bag to prevent punctures and leaks. Its most defining feature is the Grip 'n Seal technology at the top, which usually consists of a colorful plastic track (often blue or green) that creates a tactile "click" or "pop" sensation when pressed together, indicating an airtight seal. Many modern versions also feature Easy Open Tabs, which are slightly offset, textured lips at the very top that allow you to pull the bag open without straining the plastic. Some premium "Stand-Up" versions include a pleated bottom that expands when filled, allowing the bag to sit upright on a counter for easier filling with liquids like soup or marinades. The bag is clear, allowing for easy identification of contents, and often includes a white "write-on" label area for dating or labeling the items inside.