I know that I can add thickness to my hat via the "Solidify" object modifier, but my problem is that when I apply the modification, it nearly doubles the amount of faces on my mesh (it adds faces to the inside of the mesh for some reason). If I don't click apply, and still export the mesh, it applies Solidify anyway. Is there any workaround to this that isn't tedious? I'm nearly finished making my hat, and thickness is one of the last things I need to complete it.

Thanks!