Reservoir system for prolonged diffusion of an active principle

Reservoir system for prolonged and constant diffusion, in an environment which is aqueous or subjected to the action of water, of an active principle which is soluble or which can be made soluble in the said environment, characterized in that it is made, at least in part, of a nonwoven consisting of continuous monofilaments or/and of microfibers made of thermoplastic synthetic polymers, the said nonwoven being (a) treated either, if it is hydrophobic in nature, with a polysiloxane or a polymer based on polysiloxane or with a quaternary ammonium salt of amphoteric type, or, if it is hydrophilic in nature, with a perfluorinated compound or with a water-repelling agent based on an acrylic resin and paraffin, and (b) fashioned, or combined with a sheet of an impermeable material, into the shape of a closed bag containing the active principle, and in that, for a given active principle, the degree of hydrophily conferred or left on the nonwoven and the dimensions of the nonwoven which define the surface area for exchange between the internal volume and the aqueous environment for which it is intended are variable and adjusted for the desired linear release kinetics.