Netherweave Cloth

Netherweave Cloth is the next generation of cloth after.

Source
This item drops from mobs in Outland, most often from humanoids or humanoid-like creatures.

Even though nearly every humanoid mob in Outland has a good chance of dropping this cloth, a notable area for large amounts appears to be Tuurem.
 * Notable farming areas

Another option is Manaforge B'naar in Area 52. The Sunfury elves there have a 41% drop rate on cloth. They also have the added bonuses of dropping the objective of the daily Quest:Sunfury Attack Plans as well as supplying Sunfury Signets.

As an ingredient
Netherweave is used in the following recipes:

Blacksmithing

 * Adamantite Weightstone
 * Fel Weightstone

Engineering

 * Blue Smoke Flare
 * Green Smoke Flare
 * Icy Blasting Primers
 * Purple Smoke Flare
 * Red Smoke Flare
 * Super Sapper Charge
 * White Smoke Flare

First Aid

 * Netherweave Bandage
 * Heavy Netherweave Bandage

Tailoring

 * Bolt of Netherweave
 * Netherweave Net
 * Netherweave Bag