Duct tape, Duck tape: Same difference

Another one of life's little mysteries. Turns out both names are -- or have been -- correct. Check out William Safire's column in the Times Magazine: the original product was made from cotton duck cloth.

The original name of the cloth-backed, waterproof adhesive product was duck tape, developed for the United States Army by the Permacel division of Johnson & Johnson to keep moisture out of ammunition cases. The earliest civilian use I can find is in an advertisement by Gimbels department store in June 1942 (antedating the O.E.D. entry by three decades -- nobody but nobody beats this column), which substitutes our product for the ''ladder tape'' that usually holds together Venetian blinds. For $2.99, Gimbels -- now defunct -- would provide blinds ''in cream with cream tape or in white with duck tape.''
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In 1945, a government surplus property ad in The Times offered 44,108 yards of ''cotton duck tape.'' The first citation I can find for the alternative spelling is in 1970, when the Larry Plotnik Company of Chelsea, Mass., went bust and had to unload 14,000 rolls of what it advertised as duct tape. Three years later, The Times reported that to combat the infiltration of cold air, a contractor placed ''duct tape -- a fiber tape used to seal the joints in heating ducts -- over the openings.''

Here's another amusing factoid, this time from Wikipedia:

The name 'duct tape' comes from its use on heating and air conditioning ducts, a purpose for which it, ironically, has been deemed ineffective by the state of California and by building codes in most other places in the U.S....