The WEASEL Marathon rollerski offers cross-country athletes similar ski properties on two wheels thanks to optimized frame geometry, structure and material selection. With the long wheelbase and the lowered centre of gravity this rollerski leads to excellent stability and directional guidance during the gliding phase. During product design, nature served as an inspiring model, a procedure called bionics. Completely free of sharp edges and refined iteratively in a computer model, the framework transmits the load distribution in an optimal way avoiding strain peaks. The extrusion of a profile followed by CNC milling of the outer shape eliminates the need for components and connections. Thus lightness is combined with durability under high cyclic loads. The WEASEL Marathon frame shows peripheral stiffness and central flexibility, which allows for a perfect ski simulation with the best guidance without distortion. The rubber wheels designed for high loads have a rolling resistance that mimics the gliding on snow. Last but not least the visual design of the WEASEL Marathon embodies the agility and speed of its furry counterpart in its elegant white colour.