Abstract: A prepackaged closure for temporarily closing and sealing the nozzle of a dispenser cartridge includes a mass of tacky, finger-moldable sealant impermeable to volatile compounds that facilitate the fluency of the material contained in the cartridge. The mass, preferably butyl rubber, is contained in a protective package formed from separable components, the mass and container being proportioned to facilitate removal of the mass from the container. Upon removal from the container, the mass is applied and finger-molded to and about the tip of the nozzle to effect the seal.