Airtight is a system result
A lid seal only holds if the groove depth, the lid clamping force and the cord diameter agree. Changing any one of the three changes the compression, and most "the seal is bad" complaints are actually a groove that is too deep for the cord that was specified.
The joint is the weak point
Container seals are made from extruded cord cut and bonded into a ring. The bond is where failures start - a visible step, a weak join, or a misalignment that leaves a leak path. Bonding on a dedicated machine with no visible misalignment is what separates a ring that lasts from one that opens at the join.
Hardness for hand-operated lids
A lid a person closes by hand needs a softer compound than a bolted flange. Too hard and the user cannot compress it far enough; too soft and it extrudes out of the groove over time. Say how the lid is closed when you ask for a quote.
Colour for visible product
Container rings are often visible to the end user, so colour consistency and a clean surface are acceptance criteria. Pantone matching is available, and a contrasting colour helps in food plants where a fragment has to be noticed.
What to send
The groove dimensions, how much force the lid delivers, the content and the cleaning method. With those we can tell you the cord diameter and hardness that will actually seal.
Profiles for this application
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Working on something like this?
Send the drawing, cross-section, operating temperature and what the seal has to resist. We will tell you whether a stock profile fits or the part needs extruding, and quote both.