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. It functions well as a corrosion-inhibitor and lubricant for purposes that require a vacuum tight thicker lubricant. These Varian Silicon high vacuum greases are packaged in a 1/4 lbs jar and are for use with vacuum O-rings and Joints (Varian item number LGCMID025).