http://www.forumfood.org/index.php/f...W3XERt0t/5.pdf

In general, luncheon meat, wieners, and cheese should be packaged in a saran-coated nylon/polyethylene or nylon/surlyn film or EVOH barrier film. With the exception of bacon (due to its high salt content), most refrigerated products require an extremely good barrier film in order to obtain the required shelf life. The desired goals are often a minimum of 30 days for meats and six months for cheese.
Since microorganisms grow only slowly or not at all in frozen products, a medium barrier film can be used. The polyethylene or surlyn acts as a good moisture barrier to prevent dehydration and freezer burn. The nylon acts as an oxygen barrier. In the case of fresh red meats, such as beef steaks, some customers prefer to use a polypropylene/polyethylene or surlyn structure. This is commonly termed a "bloom pack" as the packaging film allows
enough oxygen to pass through it to turn the pigment myoglobin (dark red) to xymyoglobin.