There are four kinds of frost. Two common kinds of frost are fern frost and hoar frost. You see fern frost on a window pane. The ice crystals form structures which look like the fronds or leaf of a fern. Hoar frost occurs when the water vapour freezes directly onto a surface. The ice that forms may build up so that it sticks out like spikes from the surface.

Two less common frosts are rime and glazed frost. Rime forms when freezing fog touches a surface. The surface is covered with a white coating. Glazed frost forms when rain falls onto a very cold surface. The rainwater freezes and forms a thick coat of ice. This is the most dangerous kind of frost and if it builds up on power cables it can make them so heavy that they come crashing to the ground and cause power-outages.