An optical inter-satellite link gimbal 10 that is particularly suited for directing an optical beam in an optical inter-satellite communications system is disclosed. The first measuring electrode is at least partly covered by a porous material open to diffusion of the particles to be determined. A layered material is described that includes: a) a porous material comprising a porous surface; and b) a layer of blocking material comprising reactive functionalities coupled to the porous surface, wherein the interaction of the reactive functionalities with the porous material forms a diffusion blocking layer. The foam may be heated with hot air before being cooled under pressure to secure opposed plies of the partition together.