This disclosure provides a disposable mug liner fitting inside any mug or cup. The mug liner is preferably made of paper impervious to hot or cold liquids and it has a bottom and a wall. The wall is higher than the wall of the cup inside which the liner is inserted. The liner has two downward tearing lines which when torn open allow a formation of a flap that is bent over the mug handle, a hem that is bent down over the mug rim and an aperture to fit the mug handle. The liner according to this invention allows the user to keep the mug clean, protects the user from touching the mug rim and combines the convenience of a disposable cup and the sturdiness and insulation of a regular coffee mug.