External Wall Insulation Systems | JewsonExternal Wall insulation (EWI) employs a layer of insulation fixed to the exterior substrate of a building, which is then covered with a decorative and protective rendered finish. Enveloping the building in this way reduces ... insulation & Finishes. Thermal performance is dependent on the type of insulation used. To cater for all budgets and requirements, EWI systems can be used with Expanded Polystyrene, Mineral Wool, PIR or Phenolic boards. Mineral renders are extremely robust and ...