The best reflector is a parabolic and next is a curve radius A simple Stainless steel salad bowl . Making reflectore out of any thing but METAL is asking for a fire. Now note the distance from the bulb to the reflector surface must be adjusted to make max use of the light. That why parabolic reflectors have a vertical adjustment. Also note that each surface you loose 5-15% of the bulbs output. Shenells (something like that ) has a book on reflectore.
Never use plastic,paper,wood with a hid or any other bulb that get hot. Always remember that the fire dept. WILL AND DOES CALL THE COPS ON POT GROWERS, IT CHARGES THERE CHERRY. PLUS SMOKING BODYS, SMELL IS A BITCH TO GET RID OF.
LIVE safe and live longer. :glugglug: