Invisalign trays are made from SmartTrack, which is a medical-grade polyurethane thermoplastic that was created specifically for Invisalign and was approved by the Food and Drug Administration, or FDA, for use in orthodontic appliances. It’s very elastic, so when the trays are placed on the teeth, they become virtually invisible. Since Invisalign requires no brackets or wires, there’s nothing to detract from the clear appearance of the aligner trays.