weight the easy adjustability of the sealing properties also via the basis weight provides a basic advantage over the well known seal mats or liners which do not permit this adjustability in this manner in addition to the swellable fibers and for example an admixture of polypropylene and other synthetic fibers the sealing membrane can also include some so called fusion fibers in order to enable a thermal fusion of the fibers to each other the advantage of including the fusion fibers is that a higher swell pressure is obtained when the swelling fibers are moistened as a result of thermally fusing the fibers to each other after the fibers have been exposed to heat this in turn results in an increased sealing capacity in one embodiment the sealing membrane is made of a material that comprises 40 swelling fibers 50 polypropylene or other synthetic materials or fibers and 10 fusion fibers naturally the proportions of this blend can vary depending upon the intended application a basic advantage of the proposed sealing membrane is that even with repeated wet dry cycles the sealing properties of the sealing membrane remain intact for example in contrast to the known bentonite mats which can form cracks during drying cycles and exhibit subsequent leaks associated with such cracks when the mats are remoistened a further advantage of the proposed sealing membrane is that it has an optimal alkaline stability which is particularly important when the sealing layer is used in close proximity to.