The Mylar reference article from the English Wikipedia on 24-Jul-2004
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Mylar

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Mylar (a trade name in the US) is a polyethylene terephthalate polyester film used for its high tensile strength, transparency and electrical insulation. It is also known as Melinex (a trade name in the UK).

Its other common uses include:

One of its sides is slippery, the other side is microscopically rough.