Duct tape now commonly called duct tape should not be confused with special tapes actually designed for sealing heating and ventilation ducts. To provide laboratory data about which sealants and tapes last, and which are likely to fail, research was conducted at Lawrence Berkeley National Laboratory Environmental Energy Technologies Division. Their major conclusion was that one should not use common duct tape to seal ducts (they had defined duct tape as any fabric-based tape with rubber adhesive). The testing done shows that under challenging but realistic conditions, common duct tapes become brittle and may fail.
Common duct tape carries no safety certifications such as UL or Proposition 65, which means the tape may burn violently, producing toxic smoke; it may cause ingestion and contact toxicity; it can have irregular mechanical strength; and its adhesive may have low life expectancy. Its use in ducts has been prohibited by the state of California and by building codes in most other places in the US. However, higher quality metallized and aluminum tapes used by professionals for sealing ducts are still often called “duck/duct tapes”.