Do you feel puzzled about how retail bags are made?Please take several minutes to read the passage below,then you will get the answer!
 
    Presentation & Retail bags are mainly made from high clarity polypropylene or cellophane. However, polypropylene have the advantage of being less expensive than cellophane (cello) bags.

   Polypropylene film is either made under BOPP (biaxially oriented PP) or Cast film extrusion process. The major portion of this is Biaxially Oriented PP (BOPP) film, however cast films are an important segment as well.

   Bi-Oriented Polypropylene (BOPP) refers to the manufacture of polypropylene films using an orienting system. BOPP films are manufactured using a tenter frame sequential process or the double bubble process, in which a polypropylene (PP) film is oriented in two directions (machine and transverse directions). BOPP films are typically used for packaging snacks, pasta, and confectionary goods, and as collation wrap for multi-packs.

  The main features of BOPP films are improved stiffness, high tensile strength, excellent optics and good water vapour barrier properties. BOPP films range from 15 to 50 microns and are most commonly 15 to 30 microns. BOPP films can be monolayer or co-extruded structures, and transparent, opaque, or metallized. The films use mainly homopolymer PP and random copolymer PP.
 
   The ca t film process involves the extrusion of polymers melted through a slot or flat die to form a thin, molten sheet or film. This film is "pinned" to the surface of a chill roll (typically water-cooled and chrome-plated) by a blast of air from an air knife or vacuum box. The film quenches immediately and then has its edges slit prior to winding.

   Cast film extrusion offers better gauge control and gauge consistency, which are critical for thin films below 1 mil (25 microns). Lastly, optical properties such as gloss and haze percentage are typically better for any given material when produced on cast film However, it has the disadvantage of higher scrap due to edge-trim, and very little film orientation in the cross-direction.
 
   Cast films are used in a variety of markets and applications, including stretch/cling films, personal care films, bakery films, and high clarity films.