Closure for a retort processed container having a peelable seal

1. A retort capable closure in combination with a container comprising:

a. a container having a neck with a lip defining an opening therein, and a peelable seal covering said opening;

b. a closure having a top with an interior surface and a skirt depending from the top and defining a skirt interior surface;

c. at least one thread affixed to the skirt interior surface and circumscribing the skirt in a spiral such that a thread receiving groove is formed, said thread having an upper edge wherein an angle Θ is defined between the upper edge and a horizontal plane, and the angle Θ is less than about 45°;

d. a liner being made of at least a portion of vulcanized rubber and a portion of polypropylene, said liner being free from foaming agents, said liner proportioned to fit firmly within said closure and abutting the top interior surface thereof, said liner defining a resting thickness at ambient temperature and pressure conditions, and said liner being made from a material capable of being compressed to a thickness less than the resting thickness and being capable of recovering to a recovery thickness sufficient to allow said liner to maintain a positive pressure against said cap and against said seal when said cap is affixed to said container and the internal pressure of said container is raised above 0 psi and said container internal temperature is raised to above 212° F. wherein said liner maintains sufficient pressure on said peelable seal to prevent said seal from disengaging said lip during a retort operation.