David Appel was born in Washington, D.C. He obtained degrees from Leheigh University and the University of Iowa. At Iowa, he received both M.S. and Ph.D. degrees in Fluid Mechanics. He later taught and did research at the University of Iowa and later at the University of Kansas. He then joined Kimberly-Clark Corporation and applied his fluid mechanics expertise to develop new methods for making tissue. He was primarily responsible for designing and developing the crescent former type of tissue machine, which has become a standard in the industry. In recognition of his contributions, Darwin Smith, CEO of Kimberly-Clark, created the Ernst Mahler award given to recognize outstanding technical achievement. At least 14 U.S. patents list him as inventor or co-inventor. These describe not only the tissue machine, but also equipment to manufacture air-laid and nonwoven materials.