A gas turbine airfoil (20) having a load-bearing core (30). A honeycomb structure (40A, 42A) is attached to pressure and/or suction sides (22, 24) of the core and is filled with ceramic insulation (50). A ceramic matrix composite boot (60A, 60B, 60C) may cover the leading edge (26) of the core. Edges (61, 62) of the boot may be attached to the core by rows of pins (63A, 63B) or by flanges (65) inserted in slots (69) in the core. The pins may be formed in place by forming pin holes (64) in the boot, clamping the boot onto the core, filling the pin holes with metal or ceramic and metal particles, and heating the particles for internal cohesion and solid-state diffusion bonding (66) with the core. The boot may have a central portion (71) that is not bonded to the core to allow differential thermal expansion.