Punched pockets are usually transparent or semi-transparent, to allow viewing of the contents of a document without removing it. Color pockets are also available. They protect paper documents from tears, water, food, stains, and
fingerprints, and partially prevent such documents from being crumpled. Punched pockets have several holes in the left edge, which allow them to be bound into a
file folder or
ring binder. The holes in the punched pockets dispose of the difficulty of making holes in a paper
document. The most commonly used material for punched pockets is
polypropylene. However, there are some punched pockets made of
polyethylene,
cellophane, or other plastics. These may include recycled and biodegradable plastics (as defined by ASTM D5511) as well as plastics with antimicrobial additives. The clarity of the plastic will vary with the thickness of the pocket due to the
semicrystalline nature of the polymers and
light scattering by particles. Typically, biaxially-oriented polypropylene (BOPP) is used to improve clarity of punched pockets. In the UK, the most see-through punched pockets are referred to as 'glass clear' and the less clear ones as having an 'orange peel' finish. Using the customary unit of plastic thickness, the
mil ( inch), punched pockets are produced in various thicknesses for different uses, and may or may not cover both sides of the document completely. The thinnest pockets may be less than 2 mil (), while the thickest are over 4 mil (). Punched pockets are made in several sizes, with the most prevalent being
A4 () for Europe, or for the United States. Depending on the location of the opening, punched pockets may be top-loading or side-loading which dictates how the document is inserted into the pocket. Some pockets may only be sealed on two of the four sides, allowing for more convenient insertion or removal of their contents. ==Usage==