A wind turbine blade having a transition between two reinforcement fiber types is described. A gradual transition is provided by a combined double-tapered thickness section with a first type of reinforcement fibers sandwiched between a second type of reinforcement fibers or vice versa. The double-tapering is provided during layup and the reinforcement material is impregnated with a polymer resin and then cured or hardened so that the two types of reinforcement fibers are embedded in a common polymer matrix.