Mengu (men-gu) or Mempō (men-yoroi)  , is the term for various types of facial armour worn by the samurai class and their retainers in feudal Japan. Types of Japanese facial armour include the somen, menpō, hanbo or hanpo, and happuri.
Men-yoroi were facial armour which covered all or part of the face and provided a way to secure the top-heavy kabuto (helmet). The Shinobi-no-o (chin cord) of the kabuto would be tied under the chin of the men-yoroi. There were small hooks called ori-kugi or posts called odome located on various places to help secure the kabuto's chin cord. Men-yoroi may be constructed from iron or leather, or a combination of both. They may have a lacquered or rusted type of finish and can include a variety of facial details, such as moustaches, fierce teeth and a detachable nose. Most men-yoroi with the exception of the happuri had a small hole underneath the chin for sweat drainage.
Men-yoroi are similar to masks worn by armored cavalry and infantry in ancient Chinese armies from the Han Dynasty to the Song Dynasty.
Sōmen covered the entire face.