46 CFR § 153.240 - Insulation.
Cargo containment system insulation made necessary by the requirements of this part must meet the requirements in § 38.05-20 of this chapter. However, the vapor barrier required by § 38.05-20(b) is unnecessary if the insulation is:
(a) Protected from the weather, and attached to a containment system maintained at a temperature in excess of 46 °C (approx. 115 °F); or
(b) In an atmosphere whose dew point is less than the temperature of any surface in contact with the insulation.