Abstract: A laundry treating device such as a washing machine has a rotatable drum having a circumferential drum wall for placing the laundry in, a drive motor for the drum, a power control unit for supplying a drive current to the drive motor, current sensor means for supervising the drive current supplied to the drive motor, rotation position sensor means for supervising a rotation position of the drum and at least one protrusion on an inside of the circumferential drum wall. The protrusion is variable and flexible in its height over the inside of the circumferential drum wall and in its outer shape. Actuation means are provided for effecting a change of height and shape of the protrusion. Various curves for the current with varying shape of the protrusions may be recorded and compared with pre-stored reference curves for different types of laundry from various fibers.