After many many times of changing and testing, I have finally come up with this visor, which I think is quite practical.
It is a two-piece design to hold a standard 3-hole transparency film.
I made use of the elasticity of the filament so the outer piece will clamp into the inner piece so that it can hold the transparency film in position.
I tried my best to make the curvature of the front piece similar to sunglasses, so that it would feel more natural.
The plugs on both pieces allow them to lock into each other securely.
I also added an inclined surface on the back side of the inner piece, so when it is pressed on your forehead you will feel more comfortable.
Based on the individual, an elastic may be required at the back ends of the visor to fully secure it.
It can be reused, just disassemble after each use and clean it with soap and water.
COVID-19-outer-r1 legs shortened
COVID-19-visor-inner-r1 distance to transparency increased 10mm, middle hole enlarged 0.4mm for easier assembly.
COVID-19-visor-inner-r2 face in contact with forehead modified and enlarged.