First, you need room for a reflector. The Nova Extreme, I believe, has too little room around the bulbs to allow for a great reflector. The best reflective material for visible light is aluminum. The best reflective aluminum surface is a highly polished one, but the difference between really highly polished and just shiny isn't all that great. Using thin aluminum sheet, instead of foil, allows you to bend it and have it hold the shape, and it prevents the wrinkles you get with foil. A parabolic shape is the best only for point or line sources of light, which don't exist in any usable form. A reflector with flat reflective surfaces, such that you can see multiple images of the bulb when you look at it, is the best reflector of all.