A stopper adapted for attachment with a plunger rod for use within a syringe barrel, the stopper comprising: a main body portion having a roof, the main body portion defining an open rearward end configured to receive the plunger rod, the main body portion manufactured from a rigid or semi-rigid polymeric material； and a first perimetrical skirt extending around and defining a gap with respect to an outer circumference of the main body portion, wherein, when fluid pressure is increased inside the syringe barrel during an injection, the increased fluid pressure enters into the gap to cause the first perimetrical skirt to bend such that the first perimetrical skirt flexes toward the inner wall of the syringe barrel and is forced against the inner wall of the syringe barrel, and a sliding action of the plunger rod during the injection results in an engagement between the plunger rod and an engagement portion provided along an inner circumference of the main body portion which forces the main body portion to expand in the radial direction toward the inner wall of the syringe barrel.
