NOVELTY - The hollow particles consist of a resin continuous phase and a closed cell, and are thermally expandable. The particles have a durability index of 3 or less. The hollow-portion pressure of the particles is highly pressurized to a pressure environment in which the particles are used.    USE - For tire assemblies (claimed) of motor vehicles, trucks, buses, and passenger cars.    ADVANTAGE - The hollow particles provide tire assemblies having excellent high-speed durability and riding quality, and enable continuous running even when the tire receives external injury or is in punctured state.    DETAILED DESCRIPTION - The hollow particles consist of a resin continuous phase and a closed cell, and are thermally expandable. The particles have a durability index of 3 or less. The hollow-portion pressure of the particles is highly pressurized to a pressure environment in which the particles are used. The durability index is measured using a relationship given by, ((H2-H3)/H1)x100, where H1-H3 are the distances measured as follows. The inside of a container with a content volume of 50 cc having a filter at the bottom portion under atmospheric pressure is filled with hollow particles. The piston having a diameter equivalent to the diameter of the inner periphery of the container is inserted into the container and the particles are pressed. A piston plane-pressure makes a zero point the position set to 10 kPa, and the distance of the zero point and container bottom portion is set to H1. A piston plane-pressure further pushes in a piston to the position set to 200 kPa, and it continues by giving a 3 mm compression displacement to the hollow particles at a frequency of 10 Hz, making this into a reference (standard) position. H2 is the distance from the container bottom portion 150 seconds after providing start of compression displacement to the hollow-particle surface. H3 is the distance from the container bottom portion after 400 seconds to the hollow-particle surface.    An INDEPENDENT CLAIM is included for manufacture of hollow particles, which involves carrying out heating swelling of thermally-expansible resin particles containing a gas component in a resin continuous phase as foaming agent of liquid state, in a temperature range of swelling start temperature Ts1 or more, and maintaining the obtained hollow particles in an environment at a pressure exceeding atmospheric pressure and a temperature more than the inclusion-gas boiling point.    DESCRIPTION OF DRAWING(S) - The figure shows the sectional drawing of a safety tire containing sealed hollow particles.    Tire (1)    Rim (2)    Tire air chamber (3)    Hollow particles (4)    Bead core (5)