Covering Frosty is a term used to describe the phenomenon of frost forming on surfaces due to cold temperatures. RIME and HOAR are two types of frost that can form on surfaces. RIME is a white, granular deposit of ice crystals formed when water droplets in fog freeze onto objects. HOAR is a type of frost that forms when the temperature drops below freezing and the air is saturated with moisture. It is characterized by a white, feathery appearance.