Hair ice is a rare type of ice formation where the presence of a particular fungus in rotting wood produces thin strands of ice which resemble hair or candy floss. You can find out more here: Met Office

The conditions required for the formation of hair ice are extremely specific, hence the relative scarcity of sightings. 

You’ve come early to see us this year, John Frost,

Wi’ your crispin’ an’ poutherin’ gear, John Frost,

For hedge, tower, an’ tree,

As far as I see,

Are as white as the bloom o’ the pear, John Frost.

William Miller from ‘John Frost’ via Scottish Poetry Library