a dielectric insulation medium including a hydrofluoro monoether , the hydrofluoro monoether containing at least three carbon atoms . the insulation medium according has high insulation capabilities , in particular a high dielectric strength , and at the same time a low gwp . the invention further includes an insulation medium which is chemically and thermally stable also at temperatures above 140 ° c ., which is non - toxic or has a low toxicity level , and which in addition is non - corrosive and non - explosive .