Chemically, cosmoline is a Homogeneous mixture of oily and waxy long-chain, non-polar hydrocarbons. It can range in color from white to yellow, and can differ in viscosity and shear strength. Cosmoline melts at 113–125 °F (45–52 °C) and has a flashpoint of 365 °F (185 °C).
Its most common use is in the storage and preservation of firearms. Previously, cosmoline was used to preserve other items. Objects the size of entire vehicles could be preserved for future use with cosmoline.
During World War II, US Coast Artillerymen (serving the huge coastal artillery batteries) were known as "Cosmoliners" because they were tasked with the near constant cosmoline application ("greasing down") of the guns.
During Pacific island campaigns in World War II, the United States Marines sang a song about Cosmoline. Adapting the popular big-band tune "Tangerine," they would sing "Cosmoline...keeps my rifle clean."
Due to its gelatinous nature, Cosmoline can be difficult to remove completely from firearms and, as such, is being extensively replaced with vacuum-pack PET film.