Photographers use de reflector, how to do it with white cardboard!

There are no rules for the practice of reflector, as long as the area is large enough to be easy to carry. The reflector is made of white paper, but it is best to pack it with tin foil, crumple it and stick it on cardboard or plywood. The pasting method is arbitrary, as long as it can be pasted without falling off, and the better double-sided adhesive paper sold by stationery stores can also be used.

As for why it is wrinkled, it is because the reflector needs to diffuse light, so that the supplementary light is softer and will not be totally reflected like a mirror.

In the wild, sometimes there is no reflector. We can flatten it with white clothes or put it on an umbrella.