Plastic shrink wrap has become such a huge part of our lives that we take it for granted. In fact, most of us come in daily contact in one or another with this packaging method.

But how does it actual work? How does this “stuff” work

Well, it starts with the plastic polymer. Polymers are very long molecules. In fact the best analogy I can use is that the plastic polymer is like a length of Christmas lights. As we all know, a length of Christmas lights in its ”natural state” is all bunched up and tangled. In fact the more sets of lights you have, the more they are all scrambled. Plastic polymers, like Christmas lights, are naturally scrambled up and tangled.

However, shrink wrap film is manufactured so that the plastic polymers chains are oriented so that they are un-naturally stretched out. These polymer molecules are now are longer by forcing them into this awkward state. During orientation, the polymer is locked, or frozen, into its elongated state.

This straightened, longer, and oriented polymer shrink film can now be used to enclose any number of products. The only thing left to do is add the special ingredient to create the magic of shrink. In the case of shrink film the special ingredient is heat. Heat applied to the shrink film increases the molecular motion of the polymers and causes the elongated polymers to recoil, or shrink back to its natural random and disordered conformation.

Excess energy increases molecular motion (wouldn't you move if a fire were placed under your backside?). Different polymers react to this heat shrinkage differently but 50% shrinkage from the initial oriented size is not unusual. As in stretch film the tensile strength of the shrink film also increases when heated. This basic explanation applies to PVC, polyesters and polyolefin type shrink films.

So whether you are wrapping a boat, a tool, a box, or a steak remember that this poor shrink film has been manipulated unmercifully to create the final product required for your need. So now you are able to explain this great phenomenon to your kids…. Sorry I can’t help with “why is the sky blue”. That’s another web site.

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