sheathing vs wrapper

sheathing

noun
  • Something that wraps around or surrounds something, as a sheath encases its blade. 

wrapper

noun
  • Something that is wrapped around something else as a cover or protection: a wrapping. 

  • An outer garment; a loose robe or dressing gown. 

  • One who, or that which, wraps. 

  • A construct, such as a class or module, that serves to mediate access to another. 

How often have the words sheathing and wrapper occurred in a corpus of books? (source: Google Ngram Viewer )