The manufacture of plastic film for products such as food packages, shopping bags, and continuous sheeting is achieved using a blown film line. This process is the same as a regular extrusion process up until the die. There are three main types of dies used in this process: annular (or crosshead), spider, and spiral.

There are a few different types of dies used in blown film extrusion with the most common being annular, which is a simple circle die. The molten polymer enters the die head and air is injected via a hole in the die center to radially inflate the polymer into a thin tube that is many times its original, extruded diameter.

Plastic melt is extruded through an annular slit die, vertically to form thin walled tube Air is introduced in the centre of the die to blow up the tube like a balloon (IBC) Air ring blows onto the hot film to cool it (outside and inside the tube) The tube passes through nip rolls where is flattened Collapsed tube is taken back down the extrusion tower via more idler rollers On winder the tube or film is wound into rolls