About Masking
Many plastics, especially those used for displays or signs, are enshrouded in some kind of protective covering, called masking. The two most common are paper masking and poly masking (polyethylene film). LEAVE THE MASKING ON WHILE YOU CUT! If you need to draw your shape on the material first and then trace it with a tool then paper masking should be requested and there will be a bit of premium paid since paper costs more than poly film. As a general rule, poly will be shipped unless otherwise specified.
Poly-masked Polycarbonate
Paper-masked Acrylic
Remember to peel back the masking
when flame polishing
source: http://www.redwoodplastics.com/index.php?content=acrylic_care_and_maintenance
REMOVING (PAPER) MASKING
The sheet masking should be left in place during most fabrication operations to protect the sheet surface. The masking may be removed for intricate detail work on the sheet if necessary. Certain heat sources used in line bending and thermoforming operations may also require removal of the masking.
Unmasked sheet should be stored in the original shipping cartons. Avoid handling unmasked sheet unnecessarily.
You can remove the paper masking with a cardboard tube by rolling the masking around it. If the adhesive has hardened, moistening it with aliphatic naphtha, hexane or kerosene will help to soften it. Do not use gasoline or sharp-edged objects such as razor blades. Any oily film left behind by solvents should be removed immediately by washing.
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