Mastic Sealant vs Aluminum Foil Tape (For Sealing Air Ducts)

Are your ducts leaking? On average, your air ducts leak around 20-30% of your conditioned air (Energy Star). To reduce air loss and increase energy efficiency, it’s recommended that you seal all the joints and add insulation around ducts, especially in unconditioned spaces.

While you can attempt to DIY seal your air ducts, for the most comprehensive duct sealing, contact a professional HVAC technician. Learn how our PureFlow™ Duct System works.

Your technician will be able to seal all the leaks in your duct system (even the unreachable sections), but they can also clean and insulate them as well for added efficiency and improved indoor air quality.

If you don’t want to spend the money on professional duct sealing and insulation right now, consider air sealing the ducts as a DIY project using mastic sealant or HVAC tape (NOT duct tape!). Duct tape since tends to peel and doesn’t last very long.

Warning: While minor duct sealing can be performed by the homeowner, only qualified professionals should seal and insulate ducts in unconditioned spaces. If you are considering taking on duct sealing as a major project, we highly recommend a professional assessment.

Mastic Sealant

Mastic sealant is messier, but more effective. You can find this gooey duct sealant at your local home improvement store. It is usually applied with a simple paintbrush.

Depending on the leak, you may also need fiberglass mesh tape as well (gap of 1/4 inch or more). Make sure the tape matches the sealant being used.

You will need various sized paint brushes (1 inch to 3 inches), drop clothes, heavy rubber gloves, and old clothes. Some people like to use a caulk gun for the mastic, but it’s not necessary.
If there are any gaps larger than ¼ inch, use fiberglass mesh tape and mastic.

Aluminum Foil Tape

Aluminum foil tape (aka “plenum on a roll”) is easier and less messy, but it tends to fail faster due to delaminating and dirty, oily ducts. Despite the mess, mastic is more durable and preferred by most contractors.

If you do use tape, look for mastic, butyl tape, foil tape, or other heat-approved tapes that have the Underwriters Laboratories (UL) logo. High-quality HVAC tapes can be hard to find. Do your research first before purchasing the one at your home improvement store.

While professional HVAC tapes can stand the test of time, they tend to be a more expensive option than mastic sealant. Make sure you thoroughly clean the area before applying the tape. Tape tends to work better on round ductwork than the sharp and irregular corners of rectangular ducts.


Both mastic sealant and aluminum foil tape are good options for sealing air ducts. Despite the name “dust tape,” never seal air ducts with duct tape. It simply does not hold up.

No matter which sealant you choose for your ducts, make sure you choose a high-quality product and clean the application area first. If you have any doubts, don’t hesitate to Ask a Champion.

Increase energy efficiency and reduce the amount of allergens and air pollutants in your home by investing in duct sealing, insulating, and cleaning from a professional HVAC company.

Service Champions is known for trustworthy, on-time home service throughout the East Bay, South Bay, and Sacramento areas. For more information on PureFlow duct systems, call or contact us online.

Photo Credit: “Sealant Family” by Hardcast is licensed under CC BY 2.0

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