A containment arrangement for a gas turbine engine comprises: a radially outer annular casing 12; a fan track liner 28 radially within the casing comprising: an impact region 30 comprising a cellular material having a first compressive strength; at least one elongate ridge portion 26 extending through the impact region in a direction having an axial component, the ridge portion having a second compressive strength higher than the first compressive strength; and a gas-washed layer 38 radially within the fan track liner.