Non-autoclave processing of honeycomb sandwich structures generally leads to poor compaction and high porosity of the skins, along with a decreased skin-core adhesion The pressure level inside the honeycomb cells plays an important role and is controlled by the permeability to air of the skins In this work, an initial range of skin permeability to air was explored by perforating the prepregs and adhesive layer selectively The role of the resulting pressure inside the honeycomb on skin-core adhesion and skin quality was evaluated. Prepreg an permeability was found to control skin-core adhesion through the pressure in the honeycomb and potential outgassing of the adhesive layer An optimal range of initial pressure inside the honeycomb was found to be 40-70 kPa. A universal process window was proposed to determine the time flame of vacuum application leading to an optimal initial honeycomb pressure level. (C) 2010 Elsevier Ltd. All rights reserved.