A plastic bag, polybag, or pouch is a type of container made of thin, flexible, plastic film, nonwoven fabric, or plastic textile. Plastic bags are used for containing and transporting goods such as foods, produce, powders, ice, magazines, chemicals, and waste. It is a common form of packaging. Most plastic bags are heat sealed together. Some are bonded with adhesives or are stitched. Several design options and features are available. Some bags in bags store have gussets to allow a higher volume of contents. Some have the ability to stand up on a shelf or a refrigerator. Some have easy-opening or enclosable options. Handles are cut into or added into some. Bags can be made with a variety of plastics films. Polyethylene is the most common. Other forms, including laminates and co extrusions can be used when the physical properties are needed.

Depending on the construction, plastic bags can be well suited for plastic recycling. They can be incinerated in appropriate facilities for waste-to-energy conversion. They are stable and benign in sanitary landfills. If disposed of improperly, however, plastic bags can create unsightly litter and harm some types of wildlife. Bags are also made with carrying handles, hanging holes, tape attachments, or security features. Some bags have provisions for easy and controlled opening. Reclosable features, including press-to-seal zipper strips, are common for kitchen bags bought empty and for some foods. Some bags are sealed for tamper-evident capability; including some where the press-to-reseal feature becomes accessible only when a perforated outer seal is torn away.

Some bags are porous or perforated to allow the hot water to contact the food: rice, noodles, etc. Bag-in-box packaging is often used for liquids such as box wine and institutional sizes of other liquids. Plastic bags are used for many medical purposes. The non-porous quality of plastic film means that they are useful for isolating infectious body fluids; other porous bags made of nonwoven plastics can be sterilized by gas and maintain this sterility. These bags are lightweight and flexible, so they can be carried by or laid next to patients without making the patient as uncomfortable as a heavy glass bottle would be. They are less expensive than re-usable options, such as glass bottles. Plastic bags and plastic wrap are also used to prevent water loss and hypothermia in very premature babies.