The Shulhan Aruch (Orah Haim 691) rules that the Megilat Ester scroll used for fulfilling the Misva of Megila reading on Purim must be written with black ink – the same ink used for a Sefer Torah. Furthermore, it must be written on the same kind of parchment which is used for a Sefer Torah. Our Torah scrolls are generally written on the standard "Kelaf" (parchment), which is certainly acceptable for Megilat Ester, as well. The other kind of parchment – "Gevil" – is of a higher quality and may of course be used (both for a Sefer Torah and for Megilat Ester) to enhance the Misva.
It goes without saying that a Megila printed on regular paper may not be used for fulfilling the Misva of Megila reading on Purim.
The Shulhan Aruch also rules that a Megilat Ester, like a Sefer Torah, requires "Sirtut." This means that before the scribe writes the text of the Megila, he must draw straight lines across the page on the parchment to ensure that he writes the text straight. These lines must be drawn before the text is written. If the Megila text was written without "Sirtut," the Megila may not be used for the Misva, even if the lines are added afterward.
The parchment is produced from animal hide through a process called "Ibud," or tanning. When it comes to a Sefer Torah, Halacha requires that the process of "Ibud" be performed "Lishmah," meaning, with the intention that it is done for the purpose of a Torah scroll. Does this requirement apply to Megilat Ester, as well?
The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), in Hilchot Megila (2:9), writes explicitly that Megilat Ester does not require "Ibud Lishmah." In his view, one may use for Megilat Ester even a parchment that was processed for some purpose other than Megilat Ester. Rabbenu Tam (Rabbi Yaakob Tam, France, 1100-1171) disagrees, but the Shulhan Aruch accepts the Rambam’s lenient position. (The Shulhan Aruch cites Rabbenu Tam’s view as an anonymous "Yesh Omerim" position.) This ruling is, in fact, quite logical, given the fact that, as the Rambam mentions, the requirement of "Lishmah" for the parchment of a Sefer Torah applies only on the level of "De’rabbanan" – Rabbinic enactment. It therefore stands to reason that for Megila, the entire institution of which is only "De’rabbanan," we do not impose the requirement of "Lishmah."
Summary: The Megilat Ester scroll used for the reading on Purim must be written with the same kind of ink and the same kind of parchment as a Torah scroll. It must also have lines drawn on the parchment, as in the case of a Torah scroll. It differs from a Sefer Torah, however, in that the parchment used for Megilat Ester does not have to be processed with the specific intent for use as a Megila.
