The Large Backpanel is an optional accessory for Profoto's translucent umbrellas. The Backpanel is a fabric that is white on the inside and black on the outside. You attach it on the umbrella like the diffuser, in other words like a shower cap with elastic band. The result of using the Backpanel is that there will be no light leakage backwards which might influence the light quality on the subject when bouncing around. Also, as there will be less light leakage backwards, there will be more light coming thought the umbrella and on the subject. Hence it can be a good tool when having limited power on the flash unit.