The parchment upon which the torah passages are written may be processed from the hide of any Kosher animal. There are various grades of leather and types of tanning processes through which the hide is transformed into parchment.
There are two main types of processed parchment:
A. Whitened Parchment
B. Plain Parchment
A. Whitened Parchment
During the last stages of processing, the parchment is covered with a type of white paint, thus creating a smooth white surface upon which the torah passages are written. There are a number of disadvantages to this type of parchment: When the parchment is folded, as it must be when it is inserted into the Batim of the tefillin, the letters may crack (and thus be disqualified).
B. Plain Parchment
Plain parchment is a clean natural surface upon which the torah passages are written directly. This is halachically preferable.
How to distinguish between different types of parchment?
Plain parchment is slightly yellowish and not completely uniform in color, and is covered with tiny hairs. In any case, a certificate declaring that the parchment is plain should be attached.
The Torah passages < > Inserting the torah passages