Polythene is another translation for polyethylene, which is a plastic material mainly used to make plastic bags and other materials such as plastic plumbing pipes and detergent bottles. It is mainly composed of the chemical elements carbon and hydrogen. In chemistry, carbon and hydrogen molecules are bonded together in different ways, and the different classification of polythene is based on these bondings. There are ten classifications of polythene, but three of these are the ones that are used to manufacture polythene bags: MDPE (medium density polyethylene), LDPE (low density polyethylene) and VLDPE (very low density polyethylene).
Because of environmental concerns, manufacturers now produce biodegradable polythene bags that can be degraded under certain controlled conditions even though they do not naturally decompose. The two types of biodegradable polythene are starch based (hydrodegradable), which can decompose into carbon dioxide and water under certain conditions; and additive based (oxodegradable/photodegradable), which decomposes when exposed to oxygen and heat for a period of time. Because of these developments, polythene bags can become environmentally friendly bags in the future.
Polythene bags are packaged in different ways depending on where they will be used. The most common kind is the white or colored polythene bags, which are either transparent or opaque. The printed polymer bags are used as handle bags, plastic shopping bags or merchandise bags. Retail stores use these and print their logos and other information on the bags as additional advertising. Some suppliers also call these singlet bags.
The banking industry uses clear coin bags to package coins according to denominations. These types of polythene bags are thicker than what suppliers give to retail stores for their shopping bags.
Garbage bags are usually colored black or green, and vary in size and thickness depending on whether they will be used for commercial, industrial or domestic purposes.
Reclosable bags or resealable bags have a plastic ridge that closes and pulls open. They are for dry food storage since they can be refilled and resealed. Resealable bags or zipper bags also come in different sizes and can also be used for non-food items.
There are also shrink bags and stretch bags that can shrink and stretch depending on the size of their contents. Shrink bags are usually used by the food industry, especially for vacuum packing. Stretch bags are used for large packages that need to be protected from moisture, before they are placed in boxes.
Bags on a roll are mostly used in stores and homes because of their convenience. The perforated bags are attached and rolled up, so they can just be pulled out from the roll and detached easily when needed.
Aside from the food industry, textile and clothing industry and wholesale and retail stores, the medical industry also uses polythene bags for medical supplies packaging, and for medical specimen bags.
Courier and mailing services also use polythene bags for mail and packages, to protect them from water. Manufacturers place a write-on panel on these bags where the contents and address can be written on with a ballpoint pen or marker. This is very useful since plastic bags cannot be written on by ballpoint pens.