A mil is one-thousandth of an inch (0.001“or 1/1000“). The thickness of a single layer of laminating film (including both the film and the adhesive) is measured in mils. Because most lamination applications are double-sided, the actual thickness of the film is double (so a document laminated in a 3 mil pouch will actually be 6 mils thick). The smaller the mils, the thinner and less rigid the film once it’s been melted.