R Coronae Borealis stars (RCBs) provide an unique circumstellar environment that is hydrogen-deficient, helium-rich and carbon-rich in which dust condensation occurs. Litle is known about how and where the dust condensation process, compositions of the dust, and the trigger for dust formation. The hydrogen-poor carbon-rich and metal-poor (in some cases) character of the gas may facilitate the formation of dust species which are not seen in the interstellar medium or in envelopes of normal stars. Spitzer/IRS spectroscopy offers a great opportunity to characterize the infrared spectra of RCBs. Surprisingly, Spitzer has not systematically observed a complete sample of RCB stars in the previous four cycles and, thus, a comprehensive study of these dusty and fascinating stars is at present lacking. Completely inadequate spectra have been obtained from ground-based telescopes, even after nearly four decades since the discovery of the IR excess of RCB stars. We propose to obtain a library of Spitzer/IRS spectra of 18 RCB stars. Our goal is to observe stars across the chemical composition range observed in RCBs and to extend observations to the coolest RCB stars. These spectra will be complemented with the existing Spitzer/IRS spectra of 12 warmer RCB stars, creating a complete sample of 30 RCBs observed with Spitzer. Present knowledge of the dust features in RCBs depends on our previous ISO spectra of the 3 brightest RCB stars in the 3 to 25 micron region. A representative inventory of infrared spectra and dust features in our complete sample of RCB stars will provide important clues to the composition and dust formation process in these unique stars.