What a Mil Weighs Once It Is on the Tube

A mil is a thousandth of an inch, and archery is a game of grains, so the two units have to be introduced to each other before anything useful can be said about a wrap. The introduction is arithmetic, it takes one page, and it ends with a number small enough to dismiss and placed exactly where an arrow is most sensitive to it.

A thousandth of an inch, named

The mil is the trade unit of film and coating: one mil is one thousandth of an inch, which is 25.4 micrometers. A 2 mil film is therefore 50.8 micrometers thick, and a 4 mil film is 101.6. Those two figures sit in the range of a human hair, which is the comparison that makes them legible: the film of an arrow wrap is a hair to two hairs thick, spread over a band a few fingers wide.

The unit survives because it is convenient at that scale. Nobody in the film trade quotes 0.002 inches, and nobody wraps a shaft in film measured in hundredths of a millimeter. The mil keeps the numbers small and the differences legible, which is what a trade unit is for.

From thickness to mass

Thickness alone weighs nothing, so two more inputs are needed before a gram appears. The first is area: a wrap is a rectangle, and a strip 100 millimeters long and 25 millimeters wide covers 25 square centimeters. The second is density: a flexible vinyl compound in film gauge sits a little above 1.3 grams per cubic centimeter.

Mass is then area times thickness times density, and the two gauges part company. At 2 mil, the strip carries a volume of 25 times 0.00508 cubic centimeters, which is 0.127 cubic centimeters, and a mass of about 0.17 grams. At 4 mil the volume doubles and so does the mass, to about 0.33 grams. Converted into the unit archery actually counts, a grain being 0.0648 grams, the same strip is about 2.6 grains in 2 mil and about 5.1 grains in 4 mil.

What the figure is, and what it is not

Those two masses are not measurements of any product. They are the consequence of one assumed area and one assumed density, both stated so that anyone can change them. The area of a real wrap depends on the template it was cut from, and the density of a vinyl compound moves with its plasticizer content by a few percent either side of the figure used here. The desk holds none of the film sold under this domain, so it publishes the method and the range it produces, and leaves the measurement to whoever holds a sheet and a scale in the same hand.

One part of the old claim does survive the method intact. The 2019 home page said that 4 mil bumper sticker material weighs twice as much as 2 mil cast vinyl, and at equal area the arithmetic says the same thing, because doubling the thickness doubles the volume and the compound has not changed. Where the claim went further than arithmetic, the desk has left it alone.

Twelve strips, and a pack

The product description captured in 2019 said a pack held 12 printed and cut wraps. The pack figure is where the arithmetic becomes tangible: twelve strips of 2 mil film represent about two grams of vinyl, and the same twelve in 4 mil about four grams. Spread over a dozen arrows, the pack does not change anything; concentrated on one arrow, the strip is the whole question.

The pack figure also explains why the trade never had a reason to argue about it. Two grams of film in a pocket is nothing. Two and a half grains behind the nock of an arrow that has been matched to the grain is a different sentence, and it is the sentence the next section reads.

Where the grams land

A wrap is not the heaviest thing on an arrow and never will be. What makes it worth a page is position: the film sits at the tail, behind the balance point, in the region where added mass moves the balance rearward and asks the shaft to carry a little more at the end the string pushes. Added tail weight is where the desk follows that displacement, and flight and groups is where it asks what the paper target can honestly report about it.

The difference between the two figures in the table comes from the two ways a film can be made, which cast against calendered vinyl sets out. The desk keeps the figures of this page, with the assumption behind each and the date it was written down, in the spec table.