Creating a 3D structure model is the first step when using GeoDict as a virtual material lab. In most times, the first model aims to mimic the existing material. In this talk I will present how - starting from a 3D tomography image or 2D SEM images - a realistic model can be created. The first presented example consists of cellulosic fibers, i.e. curved fibers with non-circular cross section. The second example is a 60g paper. For this, the model is created by laying down the fibers on a forming fabric.