Firn

Firn (/fɪərn/; from Swiss German firn "last year's", cognate with before) is partially compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé.

[1] Firn has the appearance of wet sugar, but has a hardness that makes it extremely resistant to shovelling.

Its density generally ranges from 0.35 g/cm3 to 0.9 g/cm3,[1][2] and it can often be found underneath the snow that accumulates at the head of a glacier.

Where the crystals touch, they bond together, squeezing the air between them to the surface or into bubbles.

In colloquial and technical language, "firn" is used to describe certain forms of old snow, including: As in the last context, a ski slope that experiences melting and refreezing into harsch is said to "firn up".