The process of turning the thick hide of an ox into the batim of Tefillin includes the use of special molds under tremendous, but controlled, pressure. This makes possible the formation of a perfect square. The thickness of the leather also makes it possible to restore to the Tefillin their perfect square shape if they are damaged under special circumstances (normally, their shape does not change). Each bayit, including its lower part and the partitions of the head Tefillin, is made from a single piece of leather.
A pair of Tefillin that is made of high-quality leather from ox-skin keep their perfect square shape for many years, their color is more stable, and they are unparalleled in meeting the strictest possible requirements of the commandment of Tefillin.