Abstract: A fluid-permeable fibre matrix having a large surface area and a method of making said matrix are described. The fibre matrix is characterized in that its fibres are oriented to a high degree in such a manner that the total matrix fibre length is substantially oriented in a main orientation plane, and that membranes are provided between the fibres. It is recommended that at least 60%, preferably at least 80% of the total fibre length of the matrix deviate by at most about 20.degree. from the main orientation plane. The matrix fibres suitably consist of mineral wool, preferably glass wool, while the membranes consist of a film-forming organic or inorganic material, such as synthetic or natural polymeric materials, glass, metals, ceramics, waxes, fats or oils. The membranes may be impermeable or porous, and active material, such as inorganic catalysts, biocatalysts or adsorbing materials, such as activated carbon and zeolites, may be affixed to or incorporated in the membranes.