In Polyesters / UPR manufacturing, heat-transfer fluid performance directly affects reaction speed, color stability, molecular-weight control, and final batch consistency. Unsaturated polyester processes typically run in thermally controlled reactors where resin synthesis is commonly driven into the 200-220°C range to support esterification and polycondensation while avoiding degradation, and modern resin plants are often designed for operation up to 300°C with thermal oil circulating through external coils for heating and internal coils for cooling. In this demanding window,Eurotherm 330delivers rapid circulation, excellent low-temperature fluidity, a -49 to 315°C range, 4.04 mm²/s viscosity at 40°C, and a -68°C pour point for cold starts and flexible production changeovers.Eurotherm 320provides a cost-effective -30 to 320°C operating range with 9.8 mm²/s viscosity for mainstream reactor, reboiler, and distillation duty. For higher-temperature condensation and heavy-duty continuous service,Eurotherm 350andEurotherm THTboth extend to 350°C with low system pressure and exceptional thermal stability. In large closed-loop systems,RÜTGERS Ruetaflex 1000offers -55 to 330°C coverage with low viscosity and long service life, whileRÜTGERS Ruetasolv BP-Dadds high-temperature durability, low pour point, and strong film stability for demanding continuous resin plants seeking lower maintenance and dependable 24/7 operation.