Researchers at the SKF Engin-eering and Research Centre carried out investigations in the 1990s to test the dilution of lubricant oils with refrigerants and the consequences in bearing performance and life. In refrigerant compressors, it is difficult to avoid dilution of the oil by the refrigerant, and it is important to understand how the dilution affects rolling bearing performance. It was found that conventional all-steel bearings started to exhibit signs of inadequate lubrication at dilution levels of 20 % to 30 %. This led to the investigation of alternative bearing designs and materials to improve bearing operation and life under these poor-lubricant conditions. The studies showed that it was difficult to find a limiting dilution ratio for hybrid bearings that have steel rings and ceramic balls made of bearing grade silicon nitride (Si3N4). Finally, in 1996, hybrid bearings were run in pure refrigerant with no traces of oil, and it was found that following the feasibility test, the bearings were in as-new condition. This was a critical test result – one that opened up the possibility of using refrigerant as a lubricant for special rolling bearings. Since then, research and application development have continued and have led to several additional product features enabling reliable long-term operation.