You've extruded into air through a 0.4 nozzle and you got 0.6mm worth of die swell?? That seems excessive for any filament type.
What speed did you extrude that at?
There's just no way I could believe you could extrude into thin air through a 0.4 nozzle and end up with 1.2mm worth of swell of any material, unless it was going through an actual chemical reaction.
Something that expands THAT much after extruding would leave a monumental mess.