An oven bag is a plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 bag used for the roasting

Roasting

Roasting is a cooking method that uses dry heat, whether an open flame, oven, or other heat source. Roasting usually causes caramelization or Maillard browning of the surface of the food, which is considered by some as a flavor enhancement. Roasting uses more indirect, diffused heat , and is...

 of meat

Meat

Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...

 or other food

Food

Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

 in an oven

Oven

An oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...

. An oven bag helps to keep the food being cooked moist, by trapping the moisture in the bag and preventing it from escaping into the oven; as such, it serves a similar purpose to basting

Basting (cooking)

Basting is a cooking technique that involves cooking meat with either its own juices or some type of preparation such as a sauce or marinade. The meat is left to cook, then periodically coated with the juice....

. The plastic used for manufacture of the oven bag must be chosen so that it will not melt at the temperature during cooking and thus spoil the food.