Rubber

Rubber is an item that cannot be found naturally in the WotWs mod and instead must be created by the player. It can only be crafted by use of an Incinerator, or by crafting it from a Rubber Block which produces 9 Rubber though this must have first been crafted by a player using 9 Rubber. Rubber is produced by using an Incinerator to incinerate the six types of Minecraft Logs (Acacia, Birch, Dark Oak, Jungle, Oak and Spruce), as well as two types of logs added by the Mod, these being the Petrified Log and the Infected Log. Rubber will only be produced if the standard Logs are used. Planks, the six sided Wood variant as well as Stripped Wood and Stripped Logs will result in Ash being created instead.

Ash will also be created if the Warped or Crimson Stem is used, or in its Planks, Stripped, Hyphae or Stripped Hyphae forms. Ash Log will also result in Ash being produced by the Incinerator.

Uses
Rubber is used in the crafting recipes in only 3 crafting recipes as of the 1.2.1.1 update.

Rubber is used to produce Rubber Blocks, which is a compressed form of Rubber, much like the Netherite, Diamond, Gold and Iron Blocks of Minecraft, or the Tin, Lead, Uranium and Rock Candy Blocks the mod introduces.

Rubber can be used to produce Tire blocks, which are used in the construction of the U.S Army Jeep.

Thirdly, Rubber is used to make the Black Boots.