Drawmij's Iron Sack

This spell will provide greater protection for the contents of one normal sack or backpack. An affected sack is protected as if the interior were completely lined with inch-thick solid steel, although the sack becomes no heavier or less flexible. The sack makes its saving throws against physical or magical damage as if made of hard metal, with an additional +2 bonus to the saving throw. Items within the sack check only if the sack fails its saving throw.

The material component is a strip of leather with iron mail sewn on one side.