Mylar

Images and text by Garry Harrison,
Head, Circulating Collections Conservation,
Indiana University Libraries Preservation Department

Mylar

Mylar is mostly used for the encapsulation of flat materials. It is available in a variety of thicknesses, which are measured in "mils". The mil is not a metric unit of measure; one mil equals .001" (1/1000" or one one-thousandth of an inch). Thus, a "mil" is the same as a "point", the unit of measure used for the thickness of card and folder stock. The thickness range of the mylar we use is 2 mil to 5 mil. 2 mil is normally used for the encapsulation of small materials, such as 8.5" x 11" documents. 5 mil is used for items such as large maps and posters. Mylar can be bought in rolls, but cutting from the roll can be time-consuming, especially when dealing with large items (a full roll weighs approximately 125 lbs.). So we also keep pre-cut sheets in the following gauges/sizes:

5 mil: 50" x 50"
3 mil: 18" x 30"
2 mil: 9" x 12"

Another use for mylar is as an adhesive mask. When an adhesive-resistant mask with great strength (to facilitate removal) is needed, mylar is often the material of choice. 10 mil mylar is used in exhibit preparation by the special collections conservation unit as well.

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