Abstract: A seal of composite construction for leak testing two piece "drawn" aluminum and steel cans and three piece welded steel cans. The novel can is formed of elastomeric materials of differing hardness which are molded together to form a single, integrally formed unit. More specifically, a core formed of a soft material is disposed in sandwiched relation to working surfaces formed of a harder material so that the beneficial and detrimental characteristics of such materials are synergistically maximized and minimized, respectively. In operation, the seal is axially displaced into and out of sealing registration with the open, flanged ends of cylinders to be used as portable containers. The hard working surfaces of the seal, or pad, resist abrasion and detect microsplits, thereby overcoming the limitations of conventional soft seals, while the soft core provides the needed resiliency, thereby overcoming the limitations of conventional hard seals.