Why Does Frost Form on Windows?

What You'll Learn

• Frost is tiny ice crystals that form on cold surfaces
• It forms when the temperature drops below freezing (32°F / 0°C)
• Water vapor in the air touches the cold glass and turns directly into ice
• The ice crystals grow into beautiful patterns called frost ferns
• Frost is different from dew because dew is liquid and frost is solid ice

Words to Know

Frost

Tiny ice crystals on very cold surfaces

"Frost covered the window this morning."

Freezing

When water turns to ice (32°F/0°C)

"The glass was below freezing."

Ice crystal

A tiny piece of ice with a pattern

"Ice crystals grew on the cold glass."

Vapor

Invisible water in the air

"Water vapor turned into frost on the window."

Check What You Learned

Fun Facts

• Frost forms when water vapor deposits directly as ice on surfaces below freezing

  Source: National Weather Service / NOAA

• Freezing point is 32°F (0°C) — below this temperature, water turns solid

  Source: NWS

• Window frost occurs when indoor water vapor contacts glass that is below freezing

  Source: NOAA

• The process is called deposition — water vapor turns directly into solid ice without becoming liquid

  Source: NWS

• Frost crystals grow in branching patterns called frost ferns or ice ferns

  Source: American Meteorological Society

• Frost differs from dew: dew forms as liquid above freezing; frost forms as solid ice below freezing

  Source: NOAA