Smith & Nephew Allevyn Non Adhesive Hydrocellular Dressing. A clinically studied dressing that can stay in place for up to seven days. Perforated wound contact layer allows even viscous exudate to pass into the dressing. Hydrocellular core of the dressing absorbs and retains liquid in its microscopic structure. The breathable outer surface of the dressing allows excess moisture to evaporate away from the dressing resulting in the formation of a wound environment which allows healing to progress.