William Sherman Haynes (1864–1939) was the founder of the William S. Haynes Flute Company of Boston, alongside his brother, George.

[1][2] Haynes patented his distinctive flute design in 1914, and the company has since become a provider of silver and gold instruments to many of the world's most prominent orchestral, chamber and jazz musicians.

[3][4][5][6] High-profile soloists to have performed on a Haynes flute include Georges Barrère and Jean-Pierre Rampal.

Most notably, the company made silver, gold, and 90/10 platinum-iridium alloy flutes for Barrère.

Edgard Varèse's piece, Density 21.5, was composed for Barrère's debut on his platinum Haynes flute; 21.5 was a reference to the density of platinum.