Fire rated door

A closure comprising:

• a door configured to seal an opening, the door including a section with an internal cavity and a perforation extending between the internal cavity and a first surface of the section;
• a core within the internal cavity of the section, the core configured to expand from a relaxed state to an expanded state such that the core extends through the perforation and onto the first surface of the section when the core is in the expanded state;
• a guide coupled to an edge of the opening;
• an opening header configured to receive the door when the door is in the retracted position;
• and
• a header space between the door and the opening header when the door is in the extended position,
• wherein the door is moveable with respect to the opening along the guide from a retracted position to an extended position,
• wherein the core is configured to form a seal between the section and the guide when the core is in the expanded state, and
• wherein the section is adjacent the opening header when the door is in the extended position and the perforation confronts the header space such that the core provides a seal between the door and the opening header when the core is in the expanded state.