For archivists and conservators, acid-free means that a material has a pH level of over 7 but less than 9.5. If the board is too alkaline (over 10), the board could weaken natural protein fibres, such as silk and wool. If the board is acidic (less than 6.5), first the paper will degrade and that could damage the textiles stored within the garment box.
Lignin is the fibre in a tree that allows it to stand up. It is the second largest component of the wood part of a tree, with cellulose being the principal component. Lignin will decompose over time, releasing acidic and corrosive elements, making the paper yellow, brittle, and weak. The Kappa number measures lignin. A Kappa number of less than 5 (1% lignin) is the standard. Our paper tests to less than 5.