Article: There are primarily two kinds of plastic to choose from when it comes to creating a stencil--acetate and Mylar.  They both do the job well, it's simply a matter of preference, so check them out at your local craft store to see which appeals to you  These films come in clear and color, are available by the sheet or by the roll and some even have an adhesive backing. Check the surface to be sure it accepts pen or pencil well so that you can easily draw or trace your design.  Look for plastic that has a matte finish as this surface will typically work with graphic or ink. Acetate does have a couple of disadvantages if you're making a stencil that you plan to keep.  With time it develops a yellow or grayish cast and its edges have a tendency to curl. Repurpose your old x-rays.  Put those old plastic films to a new use as a material for your stencil design.
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Choose your plastic sheet.