The material is just baffle used to reduce turbulence within the speaker. It will sometimes move around during transport, No damage will be caused if you push this to the back.  The baffle in the bottom of this section is not fixed down during the manufacturing process but there will only ever be 1 piece within this section. The upper sections will have more of this material especially around the drivers.   If you would like more information on the design of the Revolution range please follow this link. Part 2 explains more about the cabinet design however the full series is worth a watch.