•Silica gel
•Silicon dioxide
–pure, porous,
amorphous
–chemically inert,
non-toxic, resists attrition
•high capacity > 40%
RH
•low capacity < 40%
RH
•fair capacity > 32oC
•impregnation with CoCl2:
colour change
•most common
•Activated clay
•Mined and
processed
–variation in
properties
•Oxide of silicon, aluminium,
iron and magnesium
•fair absorption
capacity at low RH
•poor capacity >32oC
•inexpensive
•specific applications