What Type Of Skin? The skin on a bodhran drum generally comes from goat. Goat is selected for drum making world wide because of its strength and flexibility. Other skins used for the bodhran include Kangaroo, Calf and rarely, Dog.
Why Treat a Skin? Skins that are untreated or over-treated for international export lack a lot of the tonal capacity that the music requires. Traditionally this is addressed by playing the drum over a period of years to 'play it in'. This means that the drum is below-optimum for a long time.
Modern bodhran skins are treated in various ways by bodhran makers to make them perform in a manner that is suitable for musical use. Typically they will be looking for low-frequency response (bass) balanced with the noise of the stick hitting the drum (attack). Bodhran makers are notoriously secretive regarding their methods of treating skins however the main treatment-objective is lubricating the skin's internal fibres so they are flexible & slippery rather than rigid & fixed.
Special Skins Some goat skins are used after having received specialist pre-treatment. One such example is the Lambeg Skin. These skins use treatments taken from the traditional way for preparing skins for the lambeg drum. The skins are also extremely thin and flexible having been closely scraped (fined). Lambeg skins have been very popular from the early 2000s and have played a large part in the development of the drum and contemporary playing styles.