Material: 3mm PLA
Hotend: original E3Dv5 0.4mm
I used a hot air gun to shape the reflector.
Heat it up carefully. You only have a few seconds until the PLA gets too weak.
1) Heat it up and form it as good as possible.
2) Glue the ends together and wait until the glue is hardened.
3) Heat it up again and lay it with the big radius flat on a surface.
4) Now you can reshape the reflector using both hands.