Nikka pellets, specially treated pieces of a natural zeolite, are used in place of silica gel to regulate the relative humidity inside packing cases. It is difficult to calculate the exact quantity of pellets needed, but it must be equivalent to a significant fraction of the mass of the contents within the case. Nikka pellets can be combined with Japanese tissue to form a humidity-buffering paper. That paper can be used in showcases, for wrapping works of art for transit, or to cover the backs of oil paintings. In the latter two cases, BO-PVA sheeting-poly(vinyl alcohol) sandwiched between two poly(vinyl chloride) films-is also used.