@helpedbytmh, you don't. But the forces of an accident compress the coat and tosses baby out of the seat. Removing the coat just shows you all the space that would be there if you were to get in an accident.

but why would you remove the coat when they're in the carseat?

what @santistevanmommie. said. There are a couple of covers that just go over the top of the car seats that are fine.
And you can test a coat to see if it's ok by strapping baby in with the coat and tightening the straps. Then take the coat off and put baby back in. If the straps are still tight, the coat is fine. If the straps are now loose, the coat is too puffy and dangerous.

Ohh okay I see now!!

@larissasentell021815, with the pad being inside the harness it causes the car seat to not function right if you were to get in an accident

Why are these covers unsafe?

Ohhh ok @santistevanmommie

@tracynangel, yeah use a thick blanket to cover baby up inside the seat but not inside the harness and then cover the top of the car seat. That's what my family always did.

So use a blanket? How to keep baby warm?