The insert material (granulate) of an adsorption dryer, sometimes called a desiccant, consisting of granules of a surface-active substance that adsorbs moisture into its pores, often generating waste heat in the process.
Examples: activated alumina, silica gel or silicon dioxide granules, molecular sieves, and activated carbon (better known for use in odour removal filter).
Below chart shows variety of adsorbent materials:
(See also, Desiccant)