Potassium Bromide (KBr) is a material commonly used in FTIR spectroscopy. KBr has a slightly larger spectral range than Sodium Chloride (NaCl) and has excellent transmission from 250nm – 26μm. Its index of refraction varies from 1.46 - 1.59 over this range. KBr is water soluble and its surfaces should be protected from exposure to moisture. Exposure to moisture will degrade the surface of the window. Potassium Bromide windows provide good resistance to mechanical shock, can be easily cleaved and can be used in temperatures up to 300°C. KBr has a density of 2.75g/cm3 and a Knoop Hardness of 7.0.