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.