A wound dressing has a base layer (2, figure 3) with an aperture 10 for locating over the wound. A top layer 3 covers the aperture and at least part of the base layer. The layers are connected discontinuously such that the wound dressing can transition from an open configuration in which the wound vents through openings 14 at its perimeter, to a closed configuration in which the top layer seals the aperture. Adhesive islands 4 may provide the connection. Alternatively, a perforated sheet (330, figure 6) and adhesive (335) are located between the base and top layer. Squeezing the adhesive through the apertures creates pillars (304) which support the top layer. The dressing may have a tab 7 as part of the base layer； the tab may be reinforced by several layers of material (16,17,18 figure 3). The base layer may carry a hydrogel adhesive (19) and a protective peel sheet (5) on its attachment surface.
