Composition of special fluid comprising at least one hydrogenated polyterpene selected from hydrogenated sesqui, di, ses-terpenes, in mixture with at least one special fluid, said special fluid being: a) a hydrocarbon mixture of petroleum origin with a cut temperature comprised between 100 and 400°C, the cut temperature being determined according to standard ASTM D86 for a final distillation point less than 365°C or according to ASTM D1160 for a final distillation point above 365°C, the distillation range being less than 75°C, or b) a hydrocarbon mixture of synthetic origin with a cut temperature comprised between 100 and 400°C, the cut temperature being determined according to standard ASTM D86 for a final distillation point less than 365°C or according to ASTM D1160 for a final distillation point above 365°C, the distillation range being less than 75°C, originating from the polymerization and/or oligomerization of olefins with 2 to 4 carbon atoms, this polymerization leading to products comprising from 2 to 5 olefin units per chain, and containing normal paraffins and iso-paraffins, or c) obtained from the conversion of natural gas and/or coal by conversion to synthesis gas, then according to the Fischer-Tropsch process, to hydrocarbon compounds capable of being separated, after hydrogenation, into distillation cuts with cuts comprised between 100 and 400°C, the cut temperature being determined according to standard ASTM D86 for a final distillation point less than 365°C or according to ASTM D1160 for a final distillation point above 365°C, the distillation range being less than 75°C, the sulphur content being less than or equal to 10 ppm and the aromatic content being less than 100 ppm. a) a hydrocarbon mixture of petroleum origin with a cut temperature comprised between 100 and 400°C, the cut temperature being determined according to standard ASTM D86 for a final distillation point less than 365°C or according to ASTM D1160 for a final distillation point above 365°C, the distillation range being less than 75°C, or b) a hydrocarbon mixture of synthetic origin with a cut temperature comprised between 100 and 400°C, the cut temperature being determined according to standard ASTM D86 for a final distillation point less than 365°C or according to ASTM D1160 for a final distillation point above 365°C, the distillation range being less than 75°C, originating from the polymerization and/or oligomerization of olefins with 2 to 4 carbon atoms, this polymerization leading to products comprising from 2 to 5 olefin units per chain, and containing normal paraffins and iso-paraffins, or c) obtained from the conversion of natural gas and/or coal by conversion to synthesis gas, then according to the Fischer-Tropsch process, to hydrocarbon compounds capable of being separated, after hydrogenation, into distillation cuts with cuts comprised between 100 and 400°C, the cut temperature being determined according to standard ASTM D86 for a final distillation point less than 365°C or according to ASTM D1160 for a final distillation point above 365°C, the distillation range being less than 75°C, the sulphur content being less than or equal to 10 ppm and the aromatic content being less than 100 ppm.