Thick Spider's Silk
Thick Spider's Silk can be looted from most level 32-60 Undead, and Beast monsters.
It can be also farmed from many species of spiders. Perhaps the best drop rates come from the Giant Plains Creepers of the Arathi Highlands at about 10%.
As an ingredient
This item is used to make:
Tailoring
[Gnomish Net-o-Matic Projector]
[Icy Cloak]
[Enchanter's Cowl]
[Swift Boots]
[Boots of the Enchanter]
[Spider Belt]
Patch changes
Patch 6.0.2 (2014-10-14): Stacks to 200, up from 10.