Abstract: Recent studies indicate that interplanetary flux ropes are low twisted. However, common magnetic field models which are used to fit them, namely constant-alpha force-free fields, have twist which increases without limit toward the flux-rope boundary. Therefore magnetic field configuration with a constant twist (set to be low) starts to be employed in fits. Real flux ropes have varying twist. We search for analytical magnetic field configurations with prescribed twist distributions in cylindrical geometry. Equations for the field solenoidality and for the force-free condition are solved for a given twist profile. The solution is applied to a core/envelope model recently suggested in studies of twist in magnetic clouds.