A vacuum system is only as good as its seals and its moving interfaces. High vacuum grease sits at those interfaces, holding pressure, lubricating rotating and sliding parts, and doing both without adding measurable vapor load to the chamber. Choosing the wrong grease shows up as a vacuum that will not pump down or a background spectrum full of contamination. Why standard lubricants fail under vacuum An ordinary oil or grease has a vapor pressure far too high for a vacuum environment. Under reduced pressure its volatile components evaporate, or outgas, raising chamber pressure, coating optics and sensors, and interfering with deposition, analysis, and coating processes. High vacuum greases are formulated from low-vapor-pressure base fluids, typically silicone, perfluoropolyether, or hydrocarbon of narrow molecular-weight distribution, so the material stays where it is applied. What high vacuum grease does Airtight sealing: it fills the microscopic surface roughness on ground-glass joints, flanges, and O-ring grooves so gas cannot leak past Friction reduction: it lubricates rotating shafts, valve stems, and sliding feedthroughs, cutting wear and torque Environmental resistance: quality grades hold up across wide temperature ranges and resist oxidation and many process chemicals Low outgassing: the defining property, keeping the grease from contributing to the chamber's gas load Where it is used Vacuum pump and valve internals, sealing and lubricating moving parts against leakage Flanges and O-rings, creating a gas-tight interface between chamber sections Rotary shaft seals and manipulators operating inside or through the vacuum boundary Laboratory equipment such as desiccators, freeze dryers, and rotary evaporators Ground-glass stopcocks and joints on gas-handling manifolds Selecting a grade Vacuum level: match the grease's vapor pressure to your target. High and ultra-high vacuum work needs a grade with vapor pressure several orders of magnitude below your base pressure to keep outgassing negligible. Material compatibility: confirm the grease will not swell or attack the elastomers, plastics, and metals in the system. Silicone grease, for example, can be a problem where silicone contamination must be avoided on downstream surfaces. Temperature range: the grease must stay in place and keep lubricating from the coldest trap to the hottest bakeout zone it will see. Chemical exposure: for systems handling reactive gases or solvents, a perfluoropolyether grease resists attack that would degrade a hydrocarbon or silicone product. Non-melting behavior: a grade that does not melt or run at elevated temperature holds a seal through thermal excursions. The Incure Pyra-Sil line Incure's Pyra-Sil 802 is a translucent silicone paste for thermal and electrical insulation and vacuum sealing. It is formulated for high vacuum service, is non-melting, and resists water and oxidation, which makes it a general-purpose choice for flanges, O-rings, and glass joints where silicone chemistry is acceptable. It is supplied in a 3 oz tube and a 453 g container. Email Us with your base pressure, temperature range, and process chemistry for a grade recommendation. Application practice Clean the sealing surfaces with a lint-free wipe and solvent, and remove all old grease before reapplying Apply a thin, continuous film; excess grease traps…