In the refrigeration system of a dehumidifier, it is generally the refrigerant piping from the evaporator outlet to the compressor inlet on the low-pressure side that needs to be insulated with cotton. This is done for several reasons: Prevent Condensation: When the surface temperature of the piping is lower than the dew point of the surrounding air, condensation may form on the surface of the pipe. Insulating with cotton can reduce this condensation phenomenon.