Place between brood boxes and honey super to keep the queen down in the brood nest and from laying in your honey super. Worker bees pass back and forth through it.
It is worth noting that there isn't any difference between a plastic queen excluder for the 10-frame wood hives or for the 10-frame polystyrene hives: it's the same queen excluder.
Fairly east to clean by freezing and then flexing a little bit (kind of like an ice cube tray).
Color may vary.