An acoustic window layer for an ultrasound array, which layer has an inner surface arranged to face the array and an outer surface arranged to face a patient, and comprising an outer layer comprising a thermoplastic polymer selected from a polyolefin family (TPO) and an elastomer selected from the polyolefin family (POE) blended therein, wherein the outer layer located at the outer surface of the acoustic window layer. In a preferred embodiment the blend comprises a copolymer of ethylene-octene and polymethylpentene. The thermoplastic polyolefin provides the blend with mechanical, chemical stability and low acoustic wave attenuation; whilst the polyolefin elastomer provides a possibility to tune the acoustic impedance of the blend and to further improve its acoustic wave propagation properties.