The reason why cellophane and corbin film are used in conjunction is even-ness.
Obviously the corbin film gathers the light toward the center (as that's it's biggest selling feature), while the cellophane/acetate/polypropylene/mylar has the light towards the outside, while the inside of the blade is dimmer. Look at an Ultrablade, you'll notice the the edges are brighter.
Combining the 2 films gives the blade a uniform/solid color that you would be unable to achieve using either film by itself.
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