I recently purchased this 2013 Lexus RX 350 and for the life of me can't determine what this rear window attachment is and what it's used for. I've done my due diligence of searching parts listings and threads in this forum. Any help is greatly appreciated. Thanks

 

I believe it is to complete the "look" of the cargo area cover. I removed my cargo area cover because we take the dogs with us frequently. I also removed that piece.
We have a 2013 RX350 as well.

 

It is the official Rear Cargo Area Useless Interference Barrier. My wife kept knocking hers off when loading and unloading for her pottery shows. So I finally took it off and carried it up to the attic where it will stay sight unseen until I re-install it just before I sell the vehicle.

 

Exactly! You don't realize the purpose till the cargo cover is pulled out.

Salim

 

Found it!! LEXUS RX350 RX450H CARGO COVER REAR DOOR EXTENSION

 

Must be for the newer models. 2010 doesn't have it?

 

Or it could be that it was never noticed. Just pull out the sliding cover and close the hatch. Peer down the back window and if you see the floor of the hatch area, then the piece in discussion is supposed to cover it. If the floor is not visible, this piece is not needed for your model.

Another approach would be to see if you have the holes in the hatch to receive the piece. See picture in post #1.

Salim

 

My 2012 RX has it.

 

It fills in the gap between the straight edge cargo cover and the curved edge of the rear door (hatch).
Remove it if your cargo is oversized, replace it when hiding cargo on a sunny day.
Trick to installing it is to start at either end and clip one after another to the other side.
It is on all 2010 through 2015 RX's

 

Thanks. Yup that’s what it is.

 

It was half detached but a little patience and I got it back on correctly