This design is based off a mix of various designs that I have tested, along with feedback from first responders who are using them. There is a version meant for attaching to the strap of your goggles and a version for attaching your own strap.
Instructions on YouTube:
Attach face shield to goggle strap - https://www.youtube.com/watch?v=63PlHBl1Bck
Attach transparency film sheet to visor part - https://www.youtube.com/watch?v=RjyGMXZSSxQ
Remove transparency film sheet from visor part - https://www.youtube.com/watch?v=CqYTGnMkKxQ
Most first responders can't decontaminate their shields in the field so they need to have a "disposable" shield that can be quickly replaced, yet stays sturdy while moving and performing duties. These shields use a sheet of transparency film (can be letter or A4) that slides in and then is locked into a slit in the visor.