Grease and solid lubricants can help protect bearings and other machine elements, but products with similar labels may use different base oils, thickeners, additives, and delivery methods. This reference compares common thickener families and solid-lubricant approaches at a practical level.

Lubricant type reference

What grease is made of

Lubricating grease is generally a base oil held in a thickener structure, with additives included for specific performance needs. The oil supplies much of the lubricating film; the thickener helps retain and release the oil. As a result, the thickener name alone does not tell you whether a grease is suitable. Base-oil viscosity, consistency, operating temperature, speed, load, water exposure, oxidation stability, and replenishment all matter.

Common soap thickeners include lithium, calcium, and sodium families. They differ in water behavior and temperature capability, and formulations vary. Polyurea is a non-soap organic thickener used in some long-life bearing greases. Clay or bentonite is an inorganic thickener used in products that may be designed for high-temperature service. These descriptions are broad family characteristics, not a substitute for a product’s published operating limits.

Solid lubricants and oil-retaining systems

Graphite and molybdenum disulfide (MoS₂) are solid lubricants that may be used where liquid lubrication is difficult or as additives in particular greases. Their usefulness depends on the contact, environment, material pairing, concentration, particle size, and method of application. A grease containing a solid additive is not automatically suitable for every rolling bearing: check bearing maker guidance and the lubricant data sheet.

Solid-oil bearing systems use a polymer matrix that retains lubricating oil around the rolling elements. This is distinct from filling a bearing with loose solid powder. The matrix can release oil during operation and absorb it again while stopped, but the complete bearing design, speed, temperature, and environment determine suitability.

Choosing and changing a lubricant

Start with the bearing manufacturer’s recommendation and the equipment duty cycle. Match the required base-oil viscosity to speed and load, then check the allowed temperature range, water resistance, oxidation life, and relubrication interval. Consider seals, contamination controls, startup conditions, and whether the lubricant can reach the contact.

Do not mix greases just because their thickener names sound similar. Compatibility depends on the exact formulations and can change consistency or oil separation. When a change is needed, consult both manufacturers, follow the equipment cleaning and purge procedure, and monitor temperature and condition. A generic family comparison cannot qualify a lubricant for a specific bearing.

Sources and limits

The family descriptions are based on the SKF bearing maintenance handbook and the National Lubricating Grease Institute explanation of grease thickeners. For solid-oil systems, see SKF’s overview of solid-oil lubrication. Consult current product documentation and the bearing maker before selection or mixing.