Plastic shrink wrap is thermoplastic extruded and oriented so that when exposed to heat, it retracts and tries to return to it's form prior to being oriented.
There are many varieties of shrink wrap films. They range from clear, thin shrink films for retail packaging to thick, heavy duty industrial shrink wrap.
High end light duty shrink films are generically known as " olefin " films. Olefins literally mean the lighter molecular weight parts of a barrel of crude oil ( naptha ). How this misnomer became to applied to shrink films is anybody's guess. Most commonly, PVC or polypropylene is blown into a bubble, reheated and blown up again, hence the slang " double bubble " label for these films. http://www.syfanusa.com/ is an example.
This is the poor man's version of Clysar http://www.clysar.com/ pioneered by DuPont. It is a multilayer film which is not only reoriented, but irradiated as well. The molecules are in a very "excitable" state, making them very sensitive to heat. These shrink films are also known as " low temperature shrink" in the meat industry. They respond well to exposure to a tepid, not even boiling, water.
The verbal shorthand for the thickness of olefin films is referred to as " ______ gauge ". All you have to remember is that every mil = 100. If you hear " 60 guage" it means 6 / 10 of a mil.
Polyethylene films with the exception of printed beverage films, are more like workhorses and not as glamorous. In terms of thickness, they pick up where olefins leave off. They are not as clear as olefins. The shrink ratios, or amount of shrink in the machine direction ( MD ) and transverse ( TD ) directions cannot be manipulated. Practically speaking, about 20% TD shrink is the best one can hope for. MD shrink is stuck at about 65%.
Watch this video to learn how to test heat shrink plastic film ratios in both MD and TD:
Because of the high amount of TD orientation, olefin shrink films have "balanced" shrink in both the MD and TD.
Industrial shrink bundling film is for unitizing cans, bottles and bags. It's natural habitat is ubiquitous in supermarkets in the early morning when shelves get stocked.
Plain PE shrink film is the dumping ground of polyethylene film. It is a convenient place to blend in scrap and rip off customers who do not know or care how to check on weights and measures. Learn how to keep your PE film supplier honest about weights and measures by watching this video:
The low per pound or roll price looks good in the office and results in inconsistent performance in the plant.
Here's a link to what most PE film extruders and distributors don't want you to know: