Packing tape, also known as parcel tape or box-sealing tape is not waterproof, however it is water resistant.
Packing tapes consist of pressure sensitive tape made from either polypropylene or polyester film and coated with pressure sensitive adhesive.
While the polypropylene or polyester make it impermeable to water it is not waterproof as the adhesive will quickly become loose when exposed to water.
Also packing tape is typically used on cardboard which can absorb water and thereby weaken the adhesive.
If you completely wrap a box in packing tape this will help keep water out however you cannot guarantee that even a fully wrapped box will remain dry if for example it is accidentally dropped in a puddle.
If you want to use packing tape to help waterproof a parcel then first completely wrap the parcel in two or three plastic bags before wrapping it in packing tape.
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