A thin elastic crust of ice, easily bending on waves and swell and under pressure, thrusting in a pattern of interlocking "fingers" (finger rafting). Has a matt surface and is up to 10cm in thickness. May be subdivided into dark nilas and light nilas.
Dark nilas is < 5cm thick and very dark in colour. Light nilas is 5-10cm thick and reflects proportionately more light than dark nilas, depending on its thickness.