Bolt of Silk Cloth is one of several types of cloth that a tailor can use to make different types of armor. It is crafted, looted and sold by NPCs.
One Hour Grind in Alterac Mountains--120 Silk Cloth Per Hour--Gold Farming in WoW Classic
Netherweave Cloth - Item - TBC Classic
Silk Cloth Farming Guide - Best places to farm Silk Cloth
Silk Cloth - Wowpedia - Your wiki guide to the World of Warcraft
Tailoring Guide 1-525 - Cataclysm Classic - Warcraft Tavern
Some WoD Crafted Armor Sets and Weapons Unobtainable in Shadowlands - Blizzard Reply - Wowhead News
Category:World of Warcraft tailoring crafted items, WoWWiki
INSANE Silk Cloth Farm Season Of Discovery Classic
Pattern: Crimson Silk Cloak - Item - World of Warcraft