Metallic soaps are the most common thickeners used in lubricating greases. Materials such as NaOH (sodium hydroxide), LIOH (lithium hydroxide), Ca(OH)2 (calcium hydroxide), and Al(OH)3 (aluminum hydroxide) contain basic or alkaline hydroxide groups (OH-). These materials are mixed with organic fatty acids in oil and heated to prepare grease. The OH- groups react with acidic H+ ions on fatty acids such as stearic acid. This reaction produces thickener fibers plus water as a by-product. This reaction is known as saponification.