Silicone Grease is a waterproof grease made by combining a silicone oil with a thickener. Silicone grease is commonly used for lubricating and preserving rubber parts, such as O-rings. Additionally, silicone grease does not swell or soften the rubber, which can be a problem with hydrocarbon based greases.Special versions of silicone grease is also used widely by the plumbing industry in faucets and seals, as well as dental equipment.