Double Seam
A double seam is formed by joining the body of the can with the lid, which in trade is usually referred to as the cover or the end. The body flange and the curl of the lid interlock together and form a strong mechanical joint. However, this joint, although strong is not yet airtight and cannot be considered to be a hermetically formed closure. A sealing compound is attached to the curl of the lid. Compressing the lid and can body together forces the soft compound sealant to flow and fill any little spaces that might be present in a double seam and the combination of a double seam and the dealing compound makes a hermetically (airtight) formed closure. The amount of the compound sealer and its composition depends on the style of container and the method of sterilization. Each double seal consists of five layers of metal interlocked together: three from the lid and two from the body of the can.