The difference from the old Calflo heat transfer fluid and the Duratherm 600 product was amazing. After an entire year of running Duratherm 600, the sludge buildup was minimal compared to Calflo after only 6 months. The performance of the Duratherm product was working so well at our plant. … I called the other plants and told them of the performance of the Duratherm. They are looking into switching over to Duratherm.