Abstract: The invention relates to a valve (2) for controlling a passage of particles from a first region (6) to a second region (7), wherein the valve (2) comprises a valve material (4) having a modifiable degree of penetrability and a valve region (16) comprising the valve material (4), wherein the valve region (16) and the valve material (4) are adapted such that the particles have to penetrate the valve material (4) if the particles pass the valve (2) for being transferred from the first region (6) to the second region (7). The degree of opening of the valve (2) can easily be controlled by modifying the degree of penetrability of the valve material (4), for example, by modifying the temperature of the valve material (4). Moreover, by penetrating the valve material (4) the particles can be separated from other elements like a fluid containing the particles.