Abstract: A writing instrument according to the present disclosure comprises a main body, a writing tip and a cap, wherein the cap is designed to be secured tightly on the main body such that the writing tip is covered by the cap. The cap comprises of an inner core and an outer layer, wherein a material of the outer layer is softer compared to a material of the inner core. With that, it is possible to design an air-tight (or almost air-tight) fitting cap for a writing instrument. With the softer outer layer of the cap, it is achieved that a user chewing on the cap has a reduced risk of damaging his/her teeth. In addition, although a membrane within the cap may still be present, such membrane is no longer necessary. The membrane may be an additional barrier contributing further to the air-tight effect of the cap that is present within the cap.