In plumbing, aluminum foil tape is used for sealing pipe insulation, creating moisture/vapor barriers, making quick temporary leak repairs on metal/plastic pipes, and sealing HVAC ductwork to improve efficiency, thanks to its excellent water resistance, heat reflectivity, and strong adhesive for durable, seamless finishes on various surfaces. It's also used for pipe lagging and creating thermal barriers in heating/cooling systems. 
Key Plumbing Uses:
Insulation & Lagging: Wrapping around pipes (hot or cold) to enhance thermal insulation, reduce heat loss/gain, and keep temperatures stable.
Sealing & Joining: Sealing joints on insulated pipes, ductwork (HVAC), and creating vapor barriers to prevent moisture ingress.
Temporary Repairs: Offering a short-term fix for small leaks in metal or plastic pipes until a permanent repair can be made.
Moisture Barrier: Its water-resistant nature makes it ideal for sealing against humidity and water vapor, preventing corrosion or damage.
Thermal Reflection: Reflecting heat away from sensitive areas or back into a space for improved energy efficiency. 
Why It's Used:
Moisture & Water Resistance: Doesn't disintegrate when exposed to moisture.
Temperature Resistant: Works in both high and low temperatures.
Durable: Provides a long-lasting, seamless finish.
Conductive: Offers thermal and electrical conductivity where needed.