Interoperable respiratory mask system

A method for protecting a user against inhalation of undesirable airborne substances within a surrounding environment, the method comprising:

• providing a respirator mask system, the respirator mask system including:
• a body having a proximal portion with a first opening to an interior, the first opening configured to accommodate the user's face, and a main portion with a second opening to the interior, the body formed from a first material,
• a casing attached to the body and configured to enclose the second opening and prevent the flow of air therethrough, the casing formed from a second material, the second material being softer than the first material,
• a filter device configured to filter out at least a portion of the undesirable airborne substances between the surrounding environment and the interior while the user is breathing,
• an accessory having a stem and configured to interact with at least the casing, at least a portion of the accessory gaining access to the interior, the stem of the accessory engaging the casing when the accessory interacts with the casing,
• a head strap configured to be placed over the head of the user;
• placing the user's face adjacent the first opening of the body, the respirator mask system configured to seal against the user's face;
• and
• securing the respirator mask system to the user by placing the head strap around the head of the user and tightening the head strap.