Writing instrument with retractable tip

A writing instrument comprising

• a barrel having a writing end opening,
• a cylinder movably disposed completely longitudinally within the barrel and having a corresponding writing end portion,
• a writing tip having a fluid dispensing element carried on said end portion of the cylinder,
• means for projecting and retracting said writing tip through the writing end opening of the barrel,
• said writing tip having a predetermined perimetric size for projection through the writing end opening of said barrel, said writing end opening having a fixed size relative to the size of the writing tip sufficient for permitting passage of said tip therethrough with clearance between said tip and said writing end opening during such projection, and a cup-shaped flexible unitary shield having an open base portion stationarily disposed within and rigidly secured to said barrel in proximity to said writing end opening and having a protruding apertured portion extending externally from the base portion and extending outwardly across the writing end opening thereof to thereby close said opening, said apertured portion having an aperture defined therein, said flexible shield being movable at said apertured portion by contact with said tip upon the projection of said tip from said barrel to expand said apertured portion and remain in contact with said fluid dispensing element and forming, when closed, a barrier against the passage of air.