To protect the rear bumper paint and plastic when loading and unloading cargo, consider installing a rear bumper guard.
There are only a few options on the market, this is what other BMW i3 owners have used:
BMW i3 Specific Rear Bumper Guard
Rear Guards in the UK has a custom molded, rigid, plastic bumper guard that protects the top surface of the bumper and also goes over the edge and slightly down to protect the edge.
Rigid ABS rear bumper guard for the BMW i3 src
Some i3 owners build their own canvas and felt version that folds out of the trunk and over the bumper for when you load and unload cargo.
I ended up buying a piece of felt big enough to fold it with four layers, then sewed the canvas on top along with a couple of tabs to tie to the cargo loops. Cost me about $10 in materials and maybe 1/2-hour labor…I just couldn’t see spending that much money for BMW’s.
jadnashuanh, BMW i3 Forum Member