Troll Leather is an item added by Ice and Fire.
There are 3 types of troll leather: Mountain, Forest and Frost. Each of them is dropped by their corresponding Troll variant.
It can be caught while fishing, as long a player has a level in Fishing Proficiency.
You can trade Sapphires for Frost Troll Leather with Craftsman Snow Villagers.
Troll Leather can be used to craft Troll Armor and Avian Saddles.