High vacuum grease is a specialty silicone-based lubricant formulated with an extremely low vapor pressure, so it resists evaporating or outgassing under vacuum conditions. It is used to lubricate and seal glass joints, stopcocks, valves, and O-rings in vacuum systems where a standard grease would break down or contaminate the system. Because it stays stable across a wide temperature range and resists most solvents, it is a standard consumable across laboratories, electronics manufacturing, and vacuum-based industrial processes.
What Is High Vacuum Grease, and How Is It Different From Standard Grease?
High vacuum grease is built on a silicone or hydrocarbon base engineered specifically for low vapor pressure and chemical inertness. Standard silicone or PTFE greases lubricate and seal perfectly well at atmospheric pressure, but under vacuum, their higher vapor pressure means small amounts of the grease evaporate (outgas) into the system. In a sealed chamber, a vacuum pump, or sensitive instrumentation, that outgassing can contaminate the environment, throw off pressure readings, or leave deposits on optical and electronic surfaces. Purpose-made high vacuum grease is formulated to minimise this effect, which is what separates it from a general-purpose lubricant.
Where Is High Vacuum Grease Used?
- Laboratory glassware — ground-glass joints, stopcocks, and desiccators, where it prevents seizing and maintains an airtight seal
- Vacuum pumps and vacuum chambers — sealing gaskets, valves, and flanges against air ingress
- Electronics and semiconductor manufacturing — sealing vacuum deposition, coating, and processing equipment
- Aerospace and analytical instrumentation — sealing connections in mass spectrometers, vacuum gauges, and similar equipment
- Pharmaceutical and food-processing vacuum equipment — freeze-dryers, vacuum ovens, and vacuum packaging lines
Key Performance Properties to Check Before You Buy
- Vapor pressure — the lower the better for high-vacuum work; this is the property that separates true vacuum grease from ordinary silicone grease
- Operating temperature range — quality vacuum grease typically performs from sub-zero temperatures up to 200°C or higher without breaking down
- Chemical inertness — should not react with glass, most plastics, or common lab solvents
- Consistency (NLGI grade) — thicker for static seals, softer for parts that need to move or rotate smoothly
- Non-melting, non-dripping behaviour — it should stay in place on a vertical or inverted joint without migrating
How to Choose the Right Grade for Your Application
Match the grade to the duty of the joint, not just the equipment type. A stopcock or valve that needs to rotate smoothly benefits from a softer, more workable grease, while a static seal under mechanical load holds up better with a firmer grade. For vacuum-level-critical work, check the manufacturer’s technical data sheet for the vapor pressure rating and confirm it matches your target vacuum range — rough vacuum, high vacuum, and ultra-high vacuum applications each have different tolerances for outgassing.
Application Best Practices
- Apply a thin, even film — over-application increases the surface area available for outgassing and can contaminate the system
- Clean the joint of old grease and residue before reapplying
- Check compatibility before use with strong oxidizers or vacuum-incompatible plastics
- Store in a sealed container away from dust and moisture to prevent contamination before use
- Reapply based on visible wear or when a joint becomes difficult to rotate, rather than on a fixed calendar schedule
High Vacuum Grease vs Standard Silicone Grease vs PTFE Grease
| Property | High Vacuum Grease | Standard Silicone Grease | PTFE Grease |
| Vapor pressure | Very low (vacuum-rated) | Moderate | Low to moderate |
| Best suited for | Vacuum systems, lab glassware | General-purpose sealing and lubrication | Plastics-safe, chemical-resistant applications |
| Temperature range | Wide (sub-zero to 200°C+) | Wide | Wide |
| Typical use | Vacuum pumps, stopcocks, chambers | O-rings, valves, general sealing | Bearings, plastic components, food-adjacent equipment |
Frequently Asked Questions
Is silicone grease safe for vacuum use?
Standard silicone grease can be used for light vacuum work, but for high or ultra-high vacuum applications, a purpose-made high vacuum grease is recommended because of its much lower vapor pressure and reduced outgassing.
How long does high vacuum grease last on a joint?
There is no fixed lifespan — it depends on how often the joint is used, temperature exposure, and whether contaminants get introduced. Most facilities reapply when a joint becomes difficult to rotate or shows visible degradation, rather than on a set schedule.
Can high vacuum grease be used on rubber O-rings?
Yes, it is compatible with most rubber and elastomer O-rings and is commonly used to extend seal life and ease installation, though it is worth checking compatibility with the specific elastomer in critical applications.
Does high vacuum grease conduct electricity?
No, high vacuum grease is electrically insulating, which makes it safe to use near most electrical and electronic components, though open contacts should still be kept clear unless the equipment manufacturer specifies otherwise.
Why Choose M R Silicone
M R Silicone (D.R.P. Silicone Industries) has manufactured silicone-based industrial lubricants since 1995, supplying consistent, batch-tested formulations to laboratories, electronics manufacturers, and industrial vacuum system operators. Get in touch for a technical data sheet or to discuss the right grade for your application.