Onionskin

Onionskin or onion skin is a thin, light-weight, strong, often translucent paper. Though not made from onions, it superficially resembles their thin, papery skins. It was usually used with carbon paper for typing duplicates in a typewriter, for permanent records where low bulk was important, or for airmail correspondence. It is typically 25–39 g/m² (9-pound basis weight in US units), and may be white or canary-colored.