Toluene diisocyanates (TDIs) are synthetic organic chemicals of low relative molecular mass (174.17). They are colourless to pale yellow liquids, at room temperature, with a distinct pungent odour detectable around 0.7 mg/rn 3 , which is well above current exposure limits. The different commercial grades solidify at between 4.7 'C and 22 'C and boil at 251 'C at 760 mmHg. Toluene diisocyanates react with water to form polyureas, carbon dioxide gas, and small amounts of diaminotoluenes, depending on the amount of water present. They also react with basic chemicals, including proteins.