A random structure in PoreXpert is a material which has no correlation in the structure a material you would expect to be modelled using a random structure is a paper or fibre based filter as the structure of the material is a woven structure with fibres of the material overlapping giving a broad pore size distribution. A random unit cell is shown in the next figure.

Example random structure in a 8 x 8 x 8 unit cell.

 

If you are working with cuboidal unit cells you are restricted to random structures.