What is this sun blocker in film making? In the making of Django Unchained, I noticed some people running behind the camera team. These people are holding something that looks like a sun blocker.

Video that shows it in use is here.

I haven't been able to confirm that or find out what this actually does.

Can anybody tell me?

Thank you!
Given the angle, I'd say it's a reflector. The line of people on the right are standing with their backs to the sun, it's probably there to bounce a bit of fill light on to their faces, so they're not silhouetted.