A breathing regulator having a non-linear positive pressure spring is provided for use in an air supplied respirator. The regulator includes a housing formed from a regulator body and a cover sub-assembly, a diaphragm assembly, and the non-linear spring. The spring holds the diaphragm assembly closed and resists the force applied by air pressure during exhalation by the user, but collapses once a sufficient amount of force has been applied, thereby permitting the user to exhale freely.