Kelim, Chapter Twenty-Three, Mishnah One
1) If a ball, a mould, an amulet or tefillin were torn, one that touches them becomes unclean,
a) But one that touches what is inside them remains clean.
2) If a saddle was torn, one that touches its contents unclean, because the stitching joins them.
Section one: The objects listed here contain something inside them. The ball contains some sort of soft filling (they didn’t fill balls with air back then). The mould is made of leather and is also filled with similar material. Artisans would craft their wares around the mould. The amulet and tefillin contain parchment with writing on it. If any of these items are torn, they are still unclean because they can still contain things inside them. A vessel which has a receptacle is impure even if it is not sealed shut. However, the contents are not considered to be connected to the vessel. Therefore, if one touches the contents and they are pure, he is still pure even if the vessel is unclean.
Section two: When it comes to a saddle, the stitching attaches the contents to the saddle. The contents are part of the saddle and not just inside the saddle. Therefore, even if the saddle is torn, a person who touches the saddle (when it is unclean) will be defiled, regardless of whether he touches the saddle or its contents.