An insulation package to reduce the transmission of heat and/or noise between the outer skin and the cabin lining of an aircraft composed of an insulating material enclosed by an encapsulating membrane. The encapsulating material has a vapor diffusion resistance (s.sub.d value) at least partially dependent on the ambient humidity, and for a gradient of relative humidity across the encapsulating membrane of 3% to 50% it has a vapor diffusion resistance (s.sub.d value) of at least 0.8 m and for a gradient of relative humidity across the encapsulating membrane of 50% to 93% it has a maximum vapor diffusion resistance (s.sub.d value) of 0.3 m.