Abstract: A hydrophobic foam insulation material is formed from a foam core material and a hydrophobic surface layer that is covalently bonded to the core, and is fully conformal to the core foam material. The surface layer is applied in a plasma. The foam material may have further been subjected to a reticulation process involving a plasma to reduce the density of the foam. Such hydrophobic insulation material is thus made lightweight, flexible, and suitable for aircraft applications.