Typewritten page of canary onionskin, 1912. Note the translucency in the upper right corner, where the red library stamp on the transverse is visible.
Onionskin or onion skin is a thin, light-weight, strong, often translucentpaper. 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 typically has a 9 pound basis weight, and may be white or canary colored.
In the typewriter era, onion skin often had a deeply textured cockle finish which allowed for easier erasure of typing mistakes, but other glazed and unglazed finishes were also available then and may be more common today.
Onionskin paper is relatively durable and lightweight due to its high content of cotton fibers. Because of these attributes and its crispness when folding, onionskin paper is one of the best papers to use for advanced paper airplanes. Paper airplanes made from onionskin paper tend to fly very well due to its low weight and high integrity once folded.