It is one of the few plastics compatible with ultra-high vacuum applications. PEEK is considered an advanced biomaterial used in medical implants, use with a high-resolution magnetic resonance imaging (MRI), for creating a partial replacement skull in neurosurgical applications. PEEK is finding increased use in spinal fusion devices and reinforcing rods. It is extensively used in the aerospace, automotive, and chemical process industries. PEEK seals and manifolds are commonly used in fluid applications. PEEK also performs well in applications where continuous high temperatures (up to 500 °F/260 °C) are common. Because of this and its low thermal conductivity, it is also used in FFF printing to thermally separate the hot end from the cold end.