The piece of PETG designed by Apple is made of three pieces - the face shield, forehead strap and silicone strap (not included). Instructions on how to assemble the shield have been posted on Apple's support website.
Apple's shields can be assembled in less than two minutes and are fully adjustable. They can be worn in two ways, regular fit and extra space.
Face shields are designed to offer protection from fluids that may contain the coronavirus, however they are designed to be worn with a face mask and other protective clothing. The device has not been tested or qualified to prevent or reduce infection, and does not provide particulate filtration.