Re: Petty or Pedant? a definitive explanation
Duck Tape is indeed a registered trademark for a variety of tapes. Also Ductape is a registered trademark of heat resistant tape designed for heating ducts.
Duck tape was a term for strips of cotton duck cloth dating to around 1900 when it did not have any adhesive. A variation was developed for waterproofing ammunition boxes in WWII.
After this, duct tape became common parlance (probably via 3M) allowing Duck Tape to be trademarked.
Generally duct tape has a strong adhesive with a fabric matrix allowing it to be torn. Gaffer's tape does not qualify because it doesn't have a strong adhesive since it is designed to be removed without leaving traces. Tape designed for hot air ducts (or Fablon) doesn't qualify because it lacks the fabric matrix and must be cut.
Finally and definitively, NASA boffins call it duct tape and it saved Apollo 13. As boffin Ed Smylie, who designed the CO2 scrubber mod, said "One thing a Southern boy will never say is, 'I don't think duct tape will fix it.'"