The color is from aluminum, a non magnetic metal. The adhesive is separate from the backing.

Duct tape relies on what’s known as a pressure-sensitive adhesive (PSA) for its inherent stickiness. PSAs are soft polymer blends that exploit van der Waals forces to join two objects together. The strength of the bond is due to the fact that the adhesive is hard enough and its viscoelastic properties are powerful enough to resist flow when stressed.

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