The filters used the the HAKKO desoldering tools and station handpieces were made from a refractory ceramic fiber, however due to regulation changes in 2015, the filter material was changed to a bio-soluble fiber and the supply of filters was completely converted by 2017. Bio-soluble fibers are a mineral fiber that readily dissolves in bodily fluids so it has a lower health concern should particles be inhaled unlike other common ceramic fibers. Bio-soluble fibers are also classified as having a low bio-persistence.
The exact composition of the material in the HAKKO filters is proprietary, but generally the minerals used to create bio-soluble fibers are calcium, magnesium, and silicate.