Netherweave Cloth

Netherweave Cloth is the next generation of cloth after Runecloth.

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 Sunfury Attack Plans (quest) 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