A seal assembly for a gas turbine engine comprising: a seal (69; 169; 269) including a main body (170; 270) extending circumferentially between opposed mate faces (178; 278), the main body (170; 270) including a sealing portion (177; 277) and an engagement portion (179; 279) extending outwardly from sealing portion (177; 277) along at least one of the mate faces (178; 278); and wherein the main body (170; 270) includes: a core (192; 292) including one or more core plies having a first fiber construction and arranged to establish an internal cavity; an overwrap (194; 294) including one or more overwrap plies having a second fiber construction and arranged to follow a perimeter of the one or more core plies to establish the engagement portion (179; 279) and the sealing portion (177; 277), and the second fiber construction differing from the first fiber construction; and characterised by the main body including a platform insert (197; 297) extending between portions of the core (192; 292) and the overwrap (194; 294) to establish the sealing portion (177; 277), and the platform insert (197; 297) including at least one intermediate ply (193; 293) having a third fiber construction differing from the first and second fiber constructions; wherein the first fiber construction establishes a first target fiber volume fraction, the second fiber construction establishes a second target fiber volume fraction, and the first and second target fiber volume fractions are equal to or greater than 0.30. a seal (69; 169; 269) including a main body (170; 270) extending circumferentially between opposed mate faces (178; 278), the main body (170; 270) including a sealing portion (177; 277) and an engagement portion (179; 279) extending outwardly from sealing portion (177; 277) along at least one of the mate faces (178; 278); and wherein the main body (170; 270) includes: a core (192; 292) including one or more core plies having a first fiber construction and arranged to establish an internal cavity; an overwrap (194; 294) including one or more overwrap plies having a second fiber construction and arranged to follow a perimeter of the one or more core plies to establish the engagement portion (179; 279) and the sealing portion (177; 277), and the second fiber construction differing from the first fiber construction; and a core (192; 292) including one or more core plies having a first fiber construction and arranged to establish an internal cavity; an overwrap (194; 294) including one or more overwrap plies having a second fiber construction and arranged to follow a perimeter of the one or more core plies to establish the engagement portion (179; 279) and the sealing portion (177; 277), and the second fiber construction differing from the first fiber construction; and characterised by the main body including a platform insert (197; 297) extending between portions of the core (192; 292) and the overwrap (194; 294) to establish the sealing portion (177; 277), and the platform insert (197; 297) including at least one intermediate ply (193; 293) having a third fiber construction differing from the first and second fiber constructions; wherein the first fiber construction establishes a first target fiber volume fraction, the second fiber construction establishes a second target fiber volume fraction, and the first and second target fiber volume fractions are equal to or greater than 0.30. extending between portions of the core (192; 292) and the overwrap (194; 294) to establish the sealing portion (177; 277), and the platform insert (197; 297) including at least one intermediate ply (193; 293) having a third fiber construction differing from the first and second fiber constructions; wherein the first fiber construction establishes a first target fiber volume fraction, the second fiber construction establishes a second target fiber volume fraction, and the first and second target fiber volume fractions are equal to or greater than 0.30.