Why laminated sheets curl and how to keep them flat

Curl comes from unequal stress: one side is laminated and the other isn't, the top and bottom films are under different tension, or the base film and the paper move differently with humidity.

One-side lamination

• Nylon base film is popular for book covers and other one-side work. Nylon breathes, so it moves with the paper as humidity changes and curls less than PET or OPP.
• Reduce unwind tension. Film stretched hot shrinks as it cools and pulls the sheet into a curl.
• Use enough heat to bond, but no more. Then let sheets cool flat before you stack them.
• Keep stock acclimated. Paper straight from a cold, damp warehouse curls more.

Two-side and heavy encapsulation

Use the same film top and bottom and balance the tension. For heavy gauges (cards, menus), some makers offer mapped and matched rolls: top and bottom rolls are paired so their stresses cancel out.

Decurler and cooling

If your laminator has a decurl bar, adjust it a little at a time. Cooling the sheet on a flat path (chill rollers or a flat table) helps more than people expect.

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