Combat Helmet (5e Equipment)
From D&D Wiki
A combat helmet is a modern military helmet made from bulletproof materials which provides protection from head injuries and shrapnel. Combat helmets are marked improvements over more ancient helmets not only because of the materials they are made from, but because they do not restrict a wearer's hearing or field of vision. Some combat helmets include a removable ballistic visor for additional protection to the face and to prevent contact with biological hazards.
Combat helmets have attachment points for night-vision devices and flashlights.
Partial armor only grants its AC bonus if you are wearing light or no armor. If you are wearing only one piece of partial armor, you are still considered to be wearing your base armor type (e.g. no armor or light armor). If you are wearing two or three pieces of partial armor, you are considered to be wearing the heaviest type of partial armor worn (e.g. medium or heavy armor). You cannot wear four or more pieces of partial armor.