Sodium Chloride (NaCl) is a material commonly used in FTIR spectroscopy. NaCl is a relatively low cost cubic crystalline material that has excellent transmission from 250nm – 16μm. Over this large spectral range, its index of refraction ranges between 1.4 - 1.6. It is hygroscopic by nature and thus samples should not contain water. Sodium Chloride windows are sensitive to thermal shock but can be used in temperatures up to 400°C. NaCl has a density of 2.17 g/cm3 and a Knoop Hardness of 18.2.