In theory aluminium tape is waterproof because water cannot penetrate the aluminium foil.
However a more accurate description of Aluminium tape would be ‘vapour retardant’.
Vapour retardant materials are used for damp proofing rather than waterproofing.
Aluminium tape prevents moisture from diffusing through walls, floors and ceilings thereby preventing the build up of water vapour from the air.
However it is not designed to patch leaks, and you certainly wouldn’t use it under water.
Aluminium tape is thin and nowhere near as sticky as other waterproof tapes, this means that if it is applied to a wet surface it is prone to trapping water underneath it which quickly causes the tape’s thin layer of glue to fail.
The best waterproofing tapes should be thick and made of a rubbery type of material that is suitable for pressing hard against a surface without bunching up and creating water pockets.
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