This flag made in blender, using cycles and cloth simulation, that's why use .blend formate for better and error free result
file info:- contains .blend [Animation + perfect matrial ] :- obj [single] :- obj animated [in zip] :- fbx [Simple] :- Stl [For Printing only]
if u like that , don't forget to rate it.
images:- wireframe + render + matirial priview + In Blender fotage
pro tip:- bake all dynamics to animate [Simple and shown in above images]