Was that an option during preorder? If so I’m sorry I missed that.Probably a part of the preorder.
If you can, put the warped mat in the sun for a few hours and it should straighten out.I just received mine as well. The second row mat got warped during shipping so I have some weight sitting on the warped piece flattening it out for a while. I’ll install them in a few days, hopefully it’ll be flattened out by then.
Interestingly I received an email mentioning Rivian cannot make the mats with the yellow logo anymore a few days before I got the shipment notification, and so I assumed they were the new all-black variant, but I got the ones with the yellow logo.
As for material, they are somewhere between fully rubberized and the plastic Weathertec and Husky use. I guess you would say they are rigid rubber. Long ago I had a pair of one piece diving flippers and the material reminds me of that.