The Impregnated Casing is a crafting component of more advanced Forestry blocks, the Apiary and Alveary. It has no use on its own. Impregnated Casings are made in a Carpenter with a 1/4 bucket of Seed Oil as the liquid.
As of 1.5.2, Creosote Oil may also be used to craft impregnated casings.
Crafting[]
To make an Impregnated Casing, you will first need to create a Carpenter, a Squeezer, and then provide a source of energy for both (Note that there may be some issues with the Buildcraft Engines as of Direwolf Update 5.2.0, if they aren't working, try a different variety of engine -- the peat-fired engine is confirmed to work with this update.)
For resources, you will need at least one stack of 64 seeds (Wheat, Flax, Chestnut, Henequen), three bars of tin to make a can, and whatever power source you'll use to fuel your engine. Place the stack(s) of seeds in the 3x3 recipe field of the squeezer, place the can(s) in the lower receptacle, and power your engine. It takes at least 50 seeds to fill one can with seed oil, and you may need more than one can of seed oil to create the impregnated casing.
For the carpenter, you'll need a stack of at least 8 logs in addition to the seed oil. The top 3x3 grid of the carpenter is merely the recipe area -- unlike crafting tables, this area does not actually take resources from your inventory. Fill each of these grid spaces with a log save for the middle, and then place your stack of logs in the lower section of the carpenter -- the one that looks similar to your own inventory. Place the seed oil cans in the top right receptacle of the carpenter, then provide the carpenter with power. It appears to take considerably less time to make the casing than it does to squeeze the seed oil.