Several factors determine a fabric's safety for use as a lining material.
Certain fibers, such as silk, are by nature acidic and should not come in direct contact with objects that are vulnerable to acid. Other fibers may emit harmful volatiles, such as sulfur compounds. Wool fabrics and felts containing wool are an example. These should be avoided. In most instances the safest fiber choice is probably cotton or linen because these fibers are by nature chemically stable.