Paper Borzoi Books
Alfred A. Knopf, a staunch firm, dabbled in the quality paperback field early on with an experiment in 1935, issuing Alcaron's The Three-Cornered Hat, Cain's The Postman Always Rings Twice, Hamsun's Hunger, Mann's Death in Venice, and Maugham's Andalusia in paperback editions at $.50. Here is the description from the Weekly Record entry for The Three-Cornered Hat:
The first volume in a new series of paper-bound editions of distinguished books issued by the publisher as "an experiment to determine whether it is economically possible to provide American readers with books of high literary quality, but without mass appeal, at low prices."
Here is what the covers looked like: https://www.bookscans.com/Oddities/borzoi.htm.
Notice, PW, Nov. 30, 1935, at 1999:
The paper bound books which Alfred A. Knopf, Inc., published in October at 50c are frankly an experiment to determine whether it's economically possible to provide American readers with books of high quality but without mass appeal at low prices. . . . The books are manufactured somewhat after the scheme of the Tauchnitz and Albatross editions but have an extra jacket which duplicates the design and coloring of the cover. They are very readable as to type and convenient to handle and carry. If the series has a fairly large sale, additional titles will be added.
Notice, PW, Feb. 29, 1936, at 994 (reporting on the sale figures of last year's paperbound experiment, Knopf is "not exactly jubilant over the outcome to date, but the experiment will be continued through the spring and if sales warrant it more books will be added to the series.")