From Plastics Wiki, free encyclopedia
Plastic wrap, known as cling-film in the United Kingdom, is a thin polymer material, roughly 0.006" (0.15mm) thick, typically used for sealing food items in containers to keep them fresh. The wrap, typically sold on rolls in boxes with a cutting edge, clings to many smooth surfaces and can thus remain tight over the opening of a container with no adhesive or other devices. Some find it difficult to use, as it both clings and tears easily. Note that plastic wrap does not tend to cling to other plastics, but it will cling to itself quite easily.
Commonly known brands of plastic wrap, in the United States, include Saran wrap and Stretch-Tite. In Australia and New Zealand, Glad wrap is the leading brand, known well enough to make its manufacturer concerned about its trademark becoming genericized.
A similar material can also be made at home by spreading clear glue on a smooth flat surface and allowing it to dry. Depending on the thickness of the layer of glue, it may tear easily, or it may be tougher and more difficult to stretch.
Plastic wrap was first made from PVC, which remains the most common material, but non-PVC alternatives are now being sold because of concerns about the transfer of plasticizers from PVC into food. It is also problematic to achieve full polymerization of the material, which can contain remains of vinyl chloride. PVC is still used because of its permeability to water vapor and oxygen, which makes it suitable for preserving meat.
The PVC-based films contain plasticizers, most often bis(2-ethylhexyl) adipate (DEHA), but phthalates (most often dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) also cause concern. The plasticizers were found to migrate to some foods, for example cheeses. In the UK, polymerized plasticizers replaced DEHP in this application, largely eliminating the problem. 
A common alternative to PVC is low density polyethylene (LDPE), which is less clingy than PVC, but also does not contain traces of potentially toxic additives. Linear low density polyethylene (LLDPE) is sometimes added to the material, as it increases the clinginess and the tensile strength of the film.  Brands like Glad Cling Wrap or Handi-Wrap are LDPE-based. Saran Premium Wrap, a newer version of Saran Wrap, is based on LDPE as well.
Glad Press'n Seal has its surface covered by microscopic spikes, preventing direct contact of the polymer surfaces, preventing it from sticking to other materials, including itself. To achieve the adhesion, the material has to be subjected to mechanical force, crushing the spikes.
PVdC has better barrier properties than more permeable LDPE, but LDPE is substantially cheaper to make.
LDPE nor PVdC are insufficiently clingy on their own, they do not adhere to themselves. To achieve the desired clinginess, certain polymers with lower molecular weight have to be added; the most common two are polyisobutene (PIB), and poly[ethylene-vinylacetate] (EVA) copolymer. Their chains readily interact with each other and their lower molecular weight makes them more mobile within the host polymer matrix. 
- "Cling film - a revolution in the food industry", European Council for Plasticisers and Intermediates (MS Word document).