Snow Trolls, Ice Trolls or Frost Trolls (Or."Borlog") were large (10-12 ft tall), rare creatures with grey-white hides and icy blue eyes that glew faintly in the dark. They could go for long periods without food, but when they saw something edible, be it a bear or a Mannish hunter, they were unstoppable.
When exposed to direct sunlight, Snow Trolls turned into huge pillars of icy slag, mysterious but fairly natural in appearance. In this form they were vulnerable to anything that banned ice: heat, sharp blows, salt — but if unharmed, they regained their normal form at nightfall. Gaunt and ghastly, Snow Trolls prowled and preyed in the northern regions of Middle-earth.