The membrane is for use with a planar surface and includes a generally planar member and a plurality of resilient tabs. The generally planar member, in use, is disposed in parallel relation to and adjacent the planar surface and, at least in use, defines a plurality of troughs, the troughs being interconnected to define a planar network of troughs that is disposed parallel to the surface, each trough presenting away from the surface in use and terminating in a common plane that is parallel to and spaced from the surface. The tabs are provided for each of one or more of the troughs, the tab lying in the common plane and spanning at least in part across said each trough.
1. A membrane for use with a planar surface, the membrane comprising a base layer defining:
a notional network of lines that cross each other to form a series of rectangles;
centrally of each rectangle, a dome having a convex surface presenting away from the base layer;
a lip peripherally surrounding each dome and being defined by: an annular concave surface presenting away from the base layer and immediately surrounding the dome; a top surface peripherally surrounding the concave surface; and a tubular surface extending from the base layer to the top surface, the tubular surface having: (i) portions that are orientated generally parallel to the sides of the rectangle in which said each dome is situated and generally perpendicular to the base layer; and (ii) adjacent each corner of the rectangle in which said each dome is situated, a portion that is angled relative to the base layer, thereby to define overhanging corners of a ridge
a plurality of protuberances, the protuberances being disposed in spaced relation to one another and to the ridges and each having: a top surface generally aligned with the surfaces of the lips; a sidewall extending from the base layer to the top surface, the sidewall having, for each of the lips immediately adjacent to such protuberance, a concave portion presenting towards such lip; and four corners defined by the junctions of the concave portions of the sidewall; and
wherein each ridge is defined in the base layer, each ridge connecting, in respect of a pair of adjacent protuberances, the immediately adjacent corners.
2. A membrane according to claim 1 , wherein:
the top surface of the lip is generally planar; and
the top surface of the protuberance is generally planar to the top surface of the lip.
3. A membrane according to claim 2 , wherein:
the top surface of the lip slopes downwardly to the concave surface;
each protuberance has a dome and a generally frustoconical surface surrounding the dome and extending upwardly and outwardly therefrom; and
the top surface of the protuberance slopes downwardly towards the frustoconical surface.