I'd suggest using buckram or even Fosshape. I've never made a hat before though, so I can't recommend a pattern for that particular shape.
Winter Palace Morrigan - Dragon Age: Inquisition (1st version finished, redoing with better materials)
M!Inquisitor Lavellan, Battlemage - Dragon Age: Inquisition
M! Knight-Commander Meredith - Dragon Age 2, on hold
F!Justice! Anders - Dragon Age 2, on hold