Rubber

Rubber is the basic component in most  recipes obtained by smelting Sticky Resin in a Furnace or an Extractor. The Extractor is the most efficient method, but it requires Electricity, so making it in a furnace is your only choice when starting out. Rubber Wood and saplings can also be converted into Rubber using an Extractor, but they yield significantly less Rubber. Rubber is primarily used in the creation of cables.

Many stacks of rubber are required in order to efficiently produce large quantities of advanced machines, so making a rubber tree farm is recommended.

An automated  farm using IC2 Rubber Trees is likely to fail due to a sapling shortage. It is, however, possible to use MFR to auto-farm RP2 Rubber Trees to great effect, given enough space to grow. This forum thread gives some vital information on how to make this work.

Note that the version of rubber used in  is basically the same as the version of rubber used in, and in Tekkit Lite can be used in the same recipes.