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I've noticed that aluminum squeeze tubes have a fold at the end. The fold is not the seal of the tube, as I can unfold and see the seal on the very end of the tube once unfolded. Wikipedia states that

Aluminium tubes generally have the far end folded several times after the contents have been added. The tube is thus hermetically sealed and nearly germ-free due to the high temperatures during the production process. The inside of the tube can be coated to prevent the material from reacting with the contents.

I don't understand why the 2nd sentence follows from the first, especially in my case where the seal is not the fold, rather it looks like the seal was made, then it was folded. Shouldn't the seal be enough to hermetically seal the tube?

Why are aluminum tubes folded at the end? How does the folding relate to hermetically sealing the tube?

jet457
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    The "thus" is misleading. Remember this was written by a member of the public not a professional copywriter. I have edited the Wiki page to substitute it with "typically", instead, to remove the implied causality. – Jonathan R Swift May 01 '20 at 11:15

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The tube is sealed in the following manner:

The aluminum from which the tube is formed is laminated or otherwise coated with a thin layer of plastic on its inside, which is easily heat-fused together and which thereby seals off the material inside from oxygen on the outside. The outer surface is also typically laminated or otherwise coated with another type of plastic to which paint will easily stick, in support of labeling the tube.

The heat-fused end can be split open if the tube is squeezed hard enough. For this reason the end of the tube is folded over on itself several times to make it harder for the heat-fused end to burst open when squeezed.

niels nielsen
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