CL20 (HNIW=Hexanitrohexaazaisowurtzitane), is an energetic molecule that presents four polymorphs (called alpha (a), beta (beta), gamma (?), and epsilon (e)). Industry is focused to synthesize the e-form. For them, it is very important to get an analytical method to quantify the concentration of the e-form, which has the best energetic performance. The aim of this work is to develop a quantitative analytical method to measure the polymorphic composition of CL20 using FTIR (mid IR and near IR, MIR/NIR) spectroscopy with PLS regression.