Disclosed is an opening system for a container that is closed with a lid, which is located under pressure. The system includes a) an arrangement suitable to allow the opening of said lid of said container; b) a flexible element suitable to be connected to said container, and suitable to be inflated; and c) a pressure-regulating subsystem suitable to produce an increase of pressure inside said container up to a value that causes the inflation of said flexible element and its tearing.

A tennis ball container for storing at least one tennis ball. The container extends along a longitudinal axis and has an open end. The container includes a removable seal enclosing the open end, and an annular overcap. The seal includes a pull tab. The overcap includes a body adapted for removably attachment to the open end of the tennis ball container. The body includes a peripheral rim for engaging an outer surface of the container at the open end, and a lip projecting from the peripheral rim toward the longitudinal axis. The lip extends over a portion of the removable seal and over a portion of the pull tab. The lip defines a first opening. The lip is configured to inhibit the at least one tennis ball from passing through the first opening. The annular overcap defines at least one breakaway region for facilitating breaking of the annular overcap.

A paper fiber-based partition or divider for use in dividing or separating products in a container that house different products is provided. A separate product container for housing one of the products may be utilized.