In geology, the frost line is the level down to which the soil will normally freeze each winter. By an analogy, the term is introduced in other areas.

• Frost line (astrophysics), a particular distance in the solar nebula from the central protosun where it is cool enough for hydrogen compounds such as water, ammonia, and methane to condense into solid ice grains.
• Frost line (polymers) in polymer film manufacturing, a notion related to physical changes from melt into solid film during extrusion.

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• Snow line
• Frost (disambiguation)
• Line (disambiguation)