This collection consists of documents pertaining to Penrose R. Hoopes' career as an engineer and inventor. Hoopes' work includes machine designs for the American Chicle Company, Campbell Soup Company, Johnson and Johnson, and the Ferracute Machine Company.

The collection is organized into four series: Project correspondence, blueprints, and related papers; Business records and promotional material; Notes, reference material, and works by Hoopes; and Professional associations.

Series I, Project correspondence, blueprints, and related papers, consists of correspondence, blueprints, blue line prints, black line prints, mechanical drawings, and photographs documenting Hoopes' professional work. The series is arranged alphabetically by firm name for seventy-eight companies for which Hoopes did consulting work for designing production machinery. They include several of the country's largest manufacturers of producers' and consumers' goods. The materials date from 1923 to 1968.

Series II, Business records and promotional material consist of resumes and applications for employment regarding Hoopes' employees, as well as employee correspondence, form letters, and promotional material in the form of pamphlets and flyers. Hoopes' correspondence with local branches of the Selective Service System includes the classification of employees during World War II. These materials date from 1923 to 1966 and are arranged alphabetically. Some materials are restricted: a 75-year time seal from the date of creation due to privacy/security reasons.

Series III, Notes, reference material, and works by Hoopes include typed and printed manuscripts relating to his two books, Early Clockmaking in Connecticut (1934) and Connecticut's Contribution to the Development of the Steamboat (1936), as well as an article, "Special Production Machinery" (1950). There are notes on eighteenth-century patents and collections of patents issued to Andrew C. Campbell and for hook-and-eye closures. Topics in this series include cams, power press design, lock nuts, orreries and clocks, early American inventors, and beauty in design. This series also includes the card catalogs of Hoopes' compiled bibliographic information on early American inventions and physical sciences. Finally, there is Hoopes' manuscript of Technical Americana, a bibliography of works on scientific invention, technology, and invention published prior to 1826, along with the index card file used in compiling the work.

Series IV, Professional associations, consists of correspondence and documents regarding Hoopes' involvement in various technical and professional associations, including the Franklin Institute.