All film has memory. I touched on this in our Cake/Taffy post where we dove into the differences in film. When you heat a film, and stretch it it wants to go back to its original shape. Contrary to popular belief wrap film can't be stretched indefinitely and does have a limit. We are going to do. a medium dive about Wrap Film & Memory in this quick entry.
Its best to stretch the film no more than 10% but you can stretch it up to 30%. So if you have 10" of film you are able to stretch it 1-3 inches. Once you do stretch it the film will want to go back to its original form. In order to prevent it from doing so you must "kill" the memory of the film.
To achieve this you have to heat the totality of the stretched film to a specified temperature. The temperature ranges from film to film but most are 190 degrees to 230 degrees. Skipping this step could result in the wrap failing & pulling back. The process of heating up the film to that range is most commonly called post heating in the wrap world.
Over stretching the film can be spotted out in the wild, it may result in discoloration, the film pulling back, or "fingers" at the edges. No amount of post heating will prevent overstretched film from pulling back. Less is more with stretching of the film.
Memory can be used as and advantage too while wrapping. Say you mess up on something and you stretched it too far, it got a wrinkle, or balled up- if you heat up the film gently it will revert back to its original shape and you are able to try again! Film WANTS to go back to the shape it was and gladly will if given the chance.
As with all things, finding that sweet spot takes time, patience, and practice. Wrapping and post heating are skills that take some finesse.
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