There are many kinds of natural and synthetic polymer systems which can be formed into packaging films. Well known examples are the cellulosics, polyolefins, polyesters, vinyls, and nylons. All of these may be formed into the thin (0.003" or less) sheets which constitute the films family. However, only a relatively few can be prepared in such a fashion that, when heat is applied, they will shrink-up in an orderly fashion.
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