My foam has two sides: one has a pattern on it while the other is flatter. Picked them in a package of five , this boards are actually made to decorate a ceiling or something like that. I'd prefer to use the foamcore if you have, first they are heavier and sturdier, second there should be less texture on the board. Well, for the moment this sort of foam works for me. So I traced a line exactly in the middle and cut them in half using cutter.
Lay them on the floor with a two to three milimeters distance so it is somewhat flexible to fold later on. And finally plaster them with a white ductape. I used a masking tape, but in the end I have to reinforced them with a thicker tape so it doesn't easily fell apart.
Et voilà, your reflector..
Here are some of the photos taken using the reflector,
You might have seen some of these photos here. What I have noticed is that since the foam has a weird bubble texture, in order to take a clear white background, I had to back up a little bit, or put the object further from the background to get just an untextured plain white backdrop.