Thermofused polypropylene felt, treated with natural anti-bacterial metal ion additives, for continuous antibacterial action. It is used as a protective layer between the AlkorPlan membrane and the surface of the swimming pool, preventing the proliferation of bacteria, fungi and microorganisms, and disguising any irregularities to the surface of the pool before applying the membrane. Rolls of 90 m2 (50 x 1,8 m).