The invention relates to an implantable valve prosthesis, optionally comprising a support structure and at least one valve leaflet. The valve prosthesis comprises a material structure of unidirectional reinforcing elements of drawn ultra high molecular weight polyolefin, extending in at least two directions, wherein the modulus of elasticity of the polyolefin reinforcing elements is at least 60 GPa. The invention furthermore relates to a method for manufacturing such an implantable valve. The valve is easily manufactured and has an improved durability.