a disposable liner is fitted against the inside surface of a sweatband of a cap or hat . the liner functions to absorb moisture and oils , and to eliminate odor . the liner wicks moisture away from a user and may hold moisture away from the hat . the liner may wick moisture to an evaporation region to be evaporated . the evaporation region may be separated from the hat by a cover layer to prevent wicking into the crown of the hat . the liner may be configured to adjust the size , and thus the fit of the hat on the head of the user . to secure a hat on the head of a user , the liner may include a compressible , foamed , polymeric core . the core may be treated with an antibacterial agent and a deodorizing agent for eliminating odors . to one side of the core is attached an adhesive layer for securing the to the sweatband of the hat . the adhesive is selected for firmness yet easy removal and disposal of the liner . the adhesive may be heat - sensitive . multiple layers of foamed polymeric substrates coated on two sides with adhesive may be adhered to one another for sizing a hat . the other side of the core is bonded to a fabric layer positionable against the forehead of a user . the fabric layer may be formed to have an absorbent layer , and may include a non - absorbent outer layer that transfers moisture but remains dry to the touch .